Yes, ranged attacks from spells are typically considered to be "weapon-like". This is definitely true of rays (and almost all ranged touch attack spells are rays) since from the rules:
You aim a ray as if using a ranged weapon
The rules further clarify that rays function as weapons for several other purposes, and the FAQ makes this very explicit:
Do rays count as weapons for the purpose of spells and effects that affect weapons?
Yes [...] rays are treated as weapons, whether they're from spells, a monster ability, a class ability, or some other source
The same rule applies to weapon-like spells such as flame blade, mage's sword, and spiritual weapon--effects that affect weapons work on these spells.
Most ranged touch attacks which aren't rays are things like acid splash -- spells where you actually throw or aim a physical object. Those are even more "weapon-like" than rays, so it's probably simplest to say all ranged touch attacks work like this.
There's another FAQ that indicates you can take "Weapon Focus (ray)" and the like; strictly speaking I guess those wouldn't apply to orb spells like acid splash.
This is all following the precedent set by 3.5; in Complete Arcane it specifies that rays and touch attack spells are "weapon-like" and thus interact with feats in the same way that other weapons do, with a split between ranged/melee type spells.
For Pathfinder, as mentioned in the comments above, Crossbow Mastery is pretty useful. Otherwise, as far as feats go, you've got 'em covered.
The Far Shot feat will turn the -2 range increment penalties into -1, which can be very useful to shoot from long range.
Here's where some cheese comes in-- when you take a 1-level dip in Rogue with the Sniper Archetype, you gain the Accuracy ability, which that further by half. This does stack RAW, which effectively doubles your range increment distance before you even see a penalty. For example, you can pick stuff off from almost half a mile away with only a -4 penalty. Granted, you'd need scrying or something to spot your targets, but your stealth check gets hilarious... Your GM will probably scowl at you for this. Pay him back by taking Leadership and Siege Engine feats... and chuck donkeys at the BBEG from the next county. On a more serious note, the Ballista is good and can be used every turn like this.
If your GM allows material from 3.5e, then you can take both Crossbow Sniper and Improved Crossbow Sniper. The former grants you half your Dex modifier to damage and a +30 feet to Sneak Attack and Skirmish ranges, and the latter bumps it up to full dex and an additional 30 feet. Furthermore, a 1-level dip in Rogue grants you a Sneak Attack, and the Craven feat from 3.5 will grant you your character level as bonus damage to SAs (at the cost of -2 will saves against fear effects).
If your GM will allow things from 3.0, you can attach a Gnome Crossbow Sight to your xbows to ignore the first two range increment penalties.
As a GM, I allow pretty much all things regarding crossbows in Pathfinder, because they're already such a sub-optimal weapon compared to bows, thanks to the absence of the strength modifier to damage and manyshot. You'll probably be using the Launching Crossbow as an Alchemist, so your experience won't be as bad as most classes, but the feat tax for using any crossbow is almost ridiculously heavy.
A little bit more cheese, but if you take a 1-level dip in Oracle, choose the Waves mystery, and take Water Sight as your first-level revelation, you'll be able to lay down Obscuring Mist a few times a day and be able to see through it without penalty. Being able to shoot with guaranteed total concealment is a huge plus to tactical fighting (its the basis for my Sniper using crossbows in my current PF game, in fact, since the concealment guarantees Sneak Attacks)
Best Answer
There is not
Clustered Shots exists because DR is a bigger problem to ranged attackers, who have fewer means of adding fixed damage to damage rolls than melee attackers, who have a built-in mechanic to increase their damage rolls (strength bonus to damage).
Normally, ranged attackers have the benefit of being able to get more attacks more easily (by not moving in the battlefield), and the way the developers found to counter-balance this was to not allow them to stack the same bonuses to damage available to melee fighters. Or, when possible, making it cost a few more feats.
Fighters have a specific feat to help bypassing damage reduction: Penetrating Strike (and Greater Penetrating Strike), which will ignore up to 5 points of a typed DR (not DR/-).
For unarmed attackers (like monks), you have the Pummeling Style feats, which will do exactly that, but that will only work with unarmed strikes. This does the same as you ask, but is very limited.