I managed to grab quite a few games from the PS1/etc/etc/etc clearance from Gamestop myself, though a vast majority of them were in generic cases or paper sleeves and scratched to shit.
This is when I learned a valuable, valuable lesson: DO NOT SELL YOUR PRIOR GEN GAMES TO FUND THE CURRENT GEN!!!!!!
Why? Because I had most of the games I rebought mangled and shit stained COMPLETE and MINTY at one point.
Mind you, I did pick up Alundra, Alundra 2, RPG Maker, Spot Goes To Hollywood and a number of other titles for UBER CHEAP, but again most were in horrid condition.
As for when they're going to dump the Xbox/GC/PS2 games no one really knows for certain, though I have been asking every time I go into a Gamestop store.
However, there's very few Xbox games I really want to rebuy, though I'd really like a complete Steel Battalion for $25(if they start @ 50% off), but the closest one to me is 80+ miles away and the stock locator isn't always 100% accurate.
With the Wii out and backwards compatible with GC games, I don't see them going anywhere anytime soon and with the PS2 now dropped to $99(according to Sony's own Playstation website) it's popularity and the popularity of it's games won't be waning anytime soon either.