Funnily enough, works by RAW.
There is no prohibition of magical healing in construct traits, though some constructs are explicitly immune to magic except select few effects.
There is also no prohibition in the heal spell.
Technically, you can do it, but expect a heavy book thrown by your DM. He will also probably houserule it away, at least I personally would.
Note:
Can't remember anything on that in 3.5 either, though the description of Warforged contrasts the possibility of both special and positive-energy healing (emphasis mine):
As living constructs, warforged can be affected by spells that target living creatures as well as by those that target constructs. Damage dealt to a warforged can be healed by a cure light wounds spell or a repair light damage spell, for example, and a warforged is vulnerable to disable construct and harm. However, spells from the healing subschool and supernatural abilities that cure hit point damage or ability damage provide only half their normal effect to a warforged.
That leads one to the implication of impossibility of positive-energy based healing for a regular construct, even if it is not stated anywhere.
The best way that I can see you improving your combat effectiveness is through the specific spells you choose.
As you had said, money is sort of tight in your campaign, so you need to make due with what you have at your disposal naturally. Luckily, this isn't hard considering that you have a +4 Cha score (Giving you anywhere between 1-4 additional spells per day at your current bonus). So considering your want to improve how well you do in combat, focus on preparing combat buff spells
These are the spells that I think you should prioritize (keep in mind that I only have the core rule book on hand):
+Bless Weapon(1st): A very situational buff, but powerful when used against the right enemies (ya did good on this one)
+Magic Weapon(1st): Prepare this instead of Bless. Bless may give you a bonus against fear, but Magic Weapon increases your damage as well as your attack bonus.
+Bull's Strength(2nd): I know that you put most of your stuff into Ranged Weapons, but everything on the list available to me is either a buff you don't need or something that seams too underhanded for a "rock star" (also, I don't think you need a spell that lets you take half of the damage that your friends take when there is a fully-functioning tank). As you may already know, Bull's Strength increases your Strength Ability by 4, so at the very least, you increase your Combat Maneuver Scores. This means it's easier to absolutely wreak an enemy's day by affecting how they move, inflicting statuses on them, or simply moving through them.
+Greater Magic Weapon(3rd): THIS is one of the key spells you should prepare when you get into the upper echelons. It's like Magic Weapon, but it gives you additional bonus amounts for every four levels your character has. Also, this spell specifically states that you can cast this spell on up to 50 arrows in the same quiver; this means that if you have to switch to another bow, or if your party also invests in bows, the spell is used to its maximum potential between multiple weapons.
+Prayer(3rd): Anyone in a 40ft radius of you receives a +/-1 to every roll depending on their loyalties; That's an increased advantage of 2 against whatever enemies you are fighting!
+Dispel Chaos/Evil(4th): these two spells give you +4 against the attacks of the designated alignment and automatically dispels effects cast by said creatures or spells that are of that alignment
This last one is just in case you attempt to build physically or your Fighter is being cornered by a Demon or something...
-Holy Sword: PROS: weapon automatically becomes +5 AND deals an additional 2d6 damage to Evil Creatures. CONS: Can only be applied to melee weapons and negates the powers of whatever weapon it is used on (that last bit could be fun to use against an enemy using an all-powerful cursed weapon, but again, this is a bit situational)
I hope this helps.
P.S.: Your party should invest in Heavy Repeating Crossbows once you hit level 10
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Best Answer
Availability
Cure Light Wounds is on spell lists of:
Those guys can all use a Wand of Cure Light Wounds without rolling Use Magic Device even if they can't cast CLW normally yet, e.g. level 1 Paladins, who don't even have Caster Levels yet. The very fact that they have it on their spell list suffices.
Infernal Healing is on spell lists of:
Since Infernal Healing has the [evil] descriptor, it is unavailable for Good Clerics, and Paladins may or may not have problems with it.
If you don't belong to any of those classes and don't cast from any of the above spell lists, the odds of meeting someone who does are a lot higher if you stick with Cure Light Wounds. On the other hand, if you can cast Infernal Healing, but not Cure Light Wounds, it might be a good idea to stick with the former. Also, if you can use the Wand of CLW but get dropped, it’s more likely that your potential savior will be able to use it than it is with Infernal Healing.
Gold per healing
One application of Cure Light Wounds costs 15 gp and heals 2 to 9 HP if cast from a Wand (5.5 HP on average). Infernal Healing always heals 10 HP per application and costs the same. On average, Infernal Healing is 82% more efficient.
Note that outside of PFS you can also craft a custom magic item that would cast CLW or Infernal Healing for you on a command word. The cost of this item would be 2,000 gp, of which you will only pay 1,000. Anyway, that's the cost of more than 2.5 level 1 wands. Usually, this won't be effective, but if you go through wand charges too quickly, it will.
Time to use
Overall, it takes 66 seconds (11 rounds) for one application of Infernal Healing to be cast upon and to end for one target. This makes Infernal Healing completely non-viable when time is limited. The more you level up, the more you have to wait to heal each time. For example, a level 6 Wizard with around 38 HP will have to wait for 42 rounds (4 minutes 12 seconds) to heal fully after being dropped to 0. The same task would require an average of 6.9 casts of CLW, or 7 rounds (1 minute 6 seconds).
On average, CLW heals 5.5 HP per round, and Infernal Healing heals pretty much 0.91 HP per round, making CLW around 6 times faster. If you start reapplying Infernal Healing the round before it is going to vanish, this number will come closer to 1 HP per round the more HP you heal, bringing the speed difference closer to 5.5 times.
Note that you can speed things up by using both spells if you need to heal a lot of HP. Not counting the first round when you cast Infernal Healing, you will cast Cure Light Wounds 9 times and then reapply Infernal Healing. Over those 10 rounds, you will heal an average or 5.5*9+10=59.5 HP instead of 55.5 HP with just Cure Light Wounds. Healing speed increases by about 7%, which may or may not matter for you, depending on the circumstances.
Also, you can apply Infernal Healing to many creatures one after another if you need to heal a lot of characters but are short on healers.
Extra utility
Extra limitations
Both of those limitations should kick in pretty rarely, but when one spell doesn't work for some reason, it's very likely that you will want the other one very much.
As noted before, Infernal Healing is also an [evil] spell. Outside of PFS, if you use it consistently over a long time period, you might turn Evil yourself, at GM's discretion. This may or may not be a downside for you, and if you are already Evil, it is clearly not.
A strict GM could rule that tinkering with evil of any kind is [Evil] and can hence affect your alignment. Another one could handwave a Good Cleric activating a Wand of Infernsl Healing because activating a wand is, for many purposes, not counted as casting a spell. Expect significant table variation.
Summary (tl;dr)
If your class has Cure Light Wounds on its spell list, but not Infernal Healing, definitely go with Cure Light Wounds first. If you buy Infernal Healing, the odds are that you will rarely get to use your Wand without UMD.
If you are a neutral Cleric or a Witch (or just use those spell lists), you might want to acquire a Wand of CLW and then a Wand of Infernal Healing, choosing the right advantage for the right situation. The same goes for evil Clerics (who are not legal in PFS). Note that Evil Clerics have no problems with casting Cure spells.
If you play in a rather stable group that has casters of both spells, you might want both wands. You will use Infernal Healing for its cost-effectiveness, and Cure Light Wounds to heal faster, or even combine them as noted before.
If you play in a stable group that can only cast Infernal Healing without UMD, buy Infernal Healing, but you still might want Cure Light Wounds for an emergency case and for healing faster once your UMD score improves.
If your stable group needs UMD for both spells... well, really make sure that you have someone, better at least two people with high UMD scores. PFS scenarios assume the players having some sort of healing available: I know that both from my own experience and from many PFS guides.
Which spell is better for you depends largely on your class and on your party composition.
Your mileage may vary greatly based upon the preferences of your local players. For example, if nobody plays Clerics, Witches, Magi, Wizards, Sorcerers, or Arcanists around your area, Infernal Healing is very unlikely to be of any use. If your party consists of 4 Wizards and you don't play with anybody else, using Cure Light Wounds will require UMD, but Infernal Healing never will.
A note on combat healing
It might be tempting to use one of the Wands in combat, but don't: it's going to be a negative game for you. Combat healing is almost never efficient in Pathfinder because usually you spend an action, but heal less than an enemy damages with one attack.
Barring an emergency (someone bleeding out), healing someone in combat can even do worse for them — someone who is down and out tends to be ignored by most enemies, but someone up with a couple HP is much more likely to get finished off in one hit.