collecting stuff

I had this idea late last night. This is just one of the many ways we could keep the player moving around and going back to places that they have already explored. I remember playing Ratchet and Clank for ps2 a few years ago and they went about collecting things in a way that makes sense I think. Basically you just had to collect gears that burst out of enemies when they die, and when you had enough you could get new guns. Now, the key is that they made the prices of the guns really high so it took some time to really do it, I found this good because games like fable for instance(if you wanted to buy the castle) didn't take very long to accomplish and it wasn't very rewarding when you did. So I think if we are gonna go the route of giving the player something to collect, it should really take awhile to do and the prize should be worth it, the reward should be on the verge of game changing, like abilities that allow you to make things much easier(like flying in kingdom hearts). Maybe we could have "region based" items in which you need to be in a certain area to collect the stuff and maybe you need a little bit from each region of the game to get the reward, like a cumulative thing. This of course is all assuming that the player has free reign over where he wants to go at a certain point in the game. I think there is something powerful about getting an item or ability and then backtracking through the game using it on places that you had missed earlier when you didn't have it. It's a lot like kingdom hearts but if we could put our own spin on it, might be worth the time.