If you don't play them anymore, go for it. You'll basically be getting $10 a piece in credit for each game, which is pretty damn good for Beyond Good And Evil, Tekken tag, Xenosaga, and Devil May Cry these days.
Plus you can easily modify the new PS2 to play imports with the Swap Magic disc.
Is it ANY five games? If you just take in two or three games, do you get partial credit? I've only got three or four games I'm thinking about taking and using for the deal.