Almost exclusively to play, there are games for older systems which I used in my youth that I'm unlikely to play using original hardware as well as a few which are just window dressing, but the games I get are for playing.
There are a few reasons my collection far exceeds my ability to get through the games as of yet:
1) Life's meant I've not had the spare time, or if the spare time exists then the energy to play games as opposed to gawping at Youtube hasn't been there.
2) System life-cycles mean that it's extremely cost effective to pick up games for systems which are 'old but not retro', as someone said here recently, it's time to fill in gaps with PS3 and 360 at the minute, the ideal time to collect obscure Wii games has arguably already passed as that system lost support earlier. The vast majority of my Xbox original games cost 50p, for instance.
3) I regularly go game hunting and am also adept at picking up non-gaming items or gaming items of value and swapping them for games or systems that I want.
4) The net has been cast wide - most action games (excluding sport and racing), RPGs (and hybrids) and anything that's not deep strategy have been fair game, up till now, so that they're there to be tried.
There are some factors which are dragging things the right way though:
1) I'm starting to make time to play.
2) The net isn't being cast as wide with current systems and I'm being much more selective in what I pick up for the systems which are currently cheap (youtube is great for getting an idea of how a game will play) and retro stuff is hard to find in the wild.
3) The way I weigh-up games is changing - in the past and during my childhood for instance, it was very easy to 'wait in hope' that a game will improve. If, after the initial few missions/levels, there isn't a massive change happening (if the game is mediocre) then that's 'it' - that's what the creators settled for, if it's not good enough then it goes.
4) Games in my least favourite action genres are going to be traded in unless they're something special, the Gears of War series for instance is going to get the chop, I've already traded in most of my Yu-Gi-Oh games and all of the Yakuzas.
5) Stuff bought cheap en-masse can be traded-in en-masse for something harder to get hold of, which will be happening.
So it's all good.