Can't help but think this idea while playing. Because it'd be great if all those guns weren't just vendor trash!
Okay, say guns have a 'potential' rating. It's like a certain number of points more damage they could do.
You charge them with, oh, lets make up a name and call them tech points! 100 tech points equals one more point of damage on a gun! When you use tech points in your inventory (they don't use up a slot though), it improves the weapon you're currently using.
Various guns in your inventory becomes charged and you can temporarily switch to them by holding down the grenade button. This wont spoil your normal equip system. Anyway, if you hit an enemy with the gun you get a tech point! If you empty the clip you get like a 50% chance at a tech point (chance reduces for guns below your level)! Best to do both! Guns in your inventory become charged, randomly, once every two minutes or so.
Also when you sell a gun at the vendor you have a 50% chance of getting a tech point. Yeah, you can still buy them back after doing this, but selling them again wont gain you another chance.
Installing 100 tech points (to gain one point of extra damage) also costs, say, $1000. This price always stays the same, but higher level guns have higher potential levels. Money actually matters...
Now every gun you find is treasure, because it all slowly increases your power!
Because we all love opening a chest which makes us more powerful.
But opening chests which just provide trash loot, which sells for money which isn't really useful at all (past level 10, who doesn't have more money than they need?)
It'd be more fun.