This is from the review at Gamespot (I am no fan of Gamespot either) and I thought this sounded cool:
The first game didn't really give you too much reason to use your weapons. If you were skilled with the wrench, you could get by without expending too much weapon ammo. Aside from this game's enemies being tougher, Ratchet & Clank: Going Commando gives you plenty of reasons to fire away. The main addition is that most of your weapons gain experience as you use them, and once you cross a certain usage threshold, you'll receive the upgraded "gold" version of that weapon. This turns your gravity bombs into mushroom cloud-laying mini-nukes, it lets you fire off three seeker rockets instead of one, and it gives you various other similar increases. Ratchet also gains experience, so, as you eliminate enemies, you'll level up and add additional segments to your life meter. You'll also find damage-reducing armor and stronger wrenches as you make your way through the game. On top of that, you'll find hidden platinum bolts throughout the game. These bolts can be taken to specific shops and traded for even more weapon upgrades, letting you add shock, acid, or lock-on effects to some of your firearms. These upgrades are cool additions, though they don't make dramatic changes to the game.