You are right,
Some first level spells are not (that) useful for first level characters
The combat rules for measuring the duration of effects (including spells) state:
When the rules refer to a "full round", they usually mean a span of time from a particular initiative count in one round to the same initiative count in the next round. Effects that last a certain number of rounds end just before the same initiative count that they began on.
(emphasis mine)
Unfortunately for our first level casters, this means that when they cast a spell which lasts only 1 round, it will fizz away immediately before they get a chance to use it.
So, why would something like this even be a Level 1 option?
First of all, there are several exceptions which makes such spells useful even for a first level character:
- Touch spells allow you to "hold the charge" until you successfully hit with them, and give you a "free" touch attack attempt as part of the action of casting the spell.
So you can attack on the same round you cast them, as well as keep trying to hit for as many following rounds as you need.
- The spell is still active during other combatants' actions on that round - both enemies and allies - this may come up when:
- Your spell can counter an enemy's action - for example, casting Unbreakable Heart on yourself will protect you from a Fear spell your enemy will cast during his action.
- You cast the spell to buff an ally (such as Sun Metal cast on your barbarian friend's axe or Unbreakable Heart cast on a confused ally, allowing him to take his turn normally)
- An enemy exposes himself to your attack of opportunity (your Sun Metal will be active and enhance your damage during his turn)
But, most importantly, some first level spells are mainly useful for casters of higher levels - but it is still better that they are first level spells, because:
- You can access them earlier - for example, Sun Metal may be cast by a 5th level ranger (caster level 2), if it was a second level spell, that ranger will have to be at least 7th level to cast it.
- You can cast them more times per day - sticking with Sun Metal as an example - a 7th level ranger can cast it 2 times per day, instead of just once if it was a second level spell.
- They don't "compete" for spell slots with the more powerful second level spells - at the end of the day, you probably wouldn't want to trade a casting of Brow Gasher or Wilderness Soldiers, just to gain the benefits of Sun Metal - it is not powerful enough to justify being a second level spell, and if it was, it probably would have never been selected by any ranger.
Hope this helps you making sense of it all...
p.s. - I'm not even trying to discuss whether casting Sun Metal is ever the optimal choice for a ranger of any level - you didn't seem to ask about that, and I normally don't care much about such issues myself, so I may not be the best user to tackle that...
For something directly equivalent to casting a buff spell and activating it as a move action I don't think is in the game but there are many means of getting spells out.
This allows you to drink a potion as a move action, especially good as spells that can take up to 1 minute to cast take effect instantaneously when imbibed. Enlarge Person therefore can take effect by the move action of the target rather than a full round action otherwise. Many Level 1 buffing spells have a duration of 1 minute per level so even a cheap CL1 potion will last long enough. It can get exponentially more expensive with higher level spells.
For weapons, these are generally most useful with offensive attacks though nothing says they must be offensive spells. For example a small dagger of spell storing does pitiful damage but may cast any level 1-3 spell into the target which could be a buffing spell for an ally. So you can get multiple spells cast in one round by effectively getting the target to cast it on themselves.
This is similar to a spell storing weapon except it doesn't have any limit on casting time. So if Adam make an unarmed strike on his friend Bob who is wearing spell storing armour loaded with Magic Circle Against Evil, Adam has such a spells cast on them. It just has to be limited to a touch spell.
Swift action Spells
So many spells are overlooked as the overwhelming majority of spells are a standard action or more to cast, yet there are a few exceptions, Dazzling Blade is a first level spell that is only a swift action to cast yet gives the ability to blind. An excellent first level buffing spell giving anyone with a weapon the capability to get out a devastating de-buff. This swift action cast can be combined with a Standard Action casting spell.
Multi Target spells
Similar to being able to get spells out quicker with a Swift Action, having a standard action go further by simultaneously buffing multiple allies eases the burden, a very popular one is Haste as it targets 1 creature per level.
This is a level 3 spell with a long casting time but the result is permanent. The way the spell is worded your party can gain the benefit of this buff simply by the item being available for all the party to touch. A very handy buff giving a 50% miss chance. This allows the effect of casting a spell by allies only investing a melee touch attack on the Symbol. You could configure the symbol to be activated by looking at it when uncovered but then enemies could benefit from it too.
General tactics:
Going Invisible can be a worthy investment if you are committed to getting out those buff spells, the spell doesn't end unless you take direct offensive action. Though what may be necessary is investing in zoning spells which delay the enemy from attacking either you or allies, this can be as direct as Web which delays most enemies a long time, or even something like Obscuring Mist, you and your allies are effectively immune inside the mist and if close together you can still see each other well enough to cast buffing spells.
Many buffing spells are so situational for allies they may want to consider the Sipping Jacket that means they can use only 1 round of a potion's duration at a time, useful for a Rogue who may occasionally need to go invisible for when their normal means of stealth otherwise fall short.
Also, if you like to use lots of pre-battle buffs, consider scrolls of Channel the Gift which means if you cast a level 1-3 spell in the next round then a spell slot isn't used up.
Best Answer
I think the only way this was ever intended to be done is through the metamagic feat Quicken Spell, as that is the only skill or feat that does explicitly state that you can still cast a spell the same round; the quickened spell you choose is a swift action, and it allows you to still cast a "regular", standard-action spell. However, the quickened spell requires a spell slot that is four spell slots higher than the spell you want to quicken.
I think there are also a select few spells that have a casting time of less than one standard action, but they really are few and far between; the only other way that comes to mind would be certain classes' Supernatural abilities, which often mimick spells, but sometimes use less than a standard action. If they allow you to cast another spell that round depends on the skill description, though.
The reason most skills that allow you to cast a spell faster than it was intended do not allow the casting of another spell that round, is simply to avoid abuse: If you were allowed to do that, you could cast another quickened spell and another standard action spell the same round, which gives you a total of three spells per round that you can cast, which clearly would be OP.