I have been working on collecting at least of of every card, and I've got most of them already. This means that hordes of my cards are never used. So I let people build decks for fun play out of my cards. For example, right now, I have 5 people who each have at least 2 decks built out of my cards. The result is that even though some cards, like the Skyshroud Behemoth don't work in the local tournaments, they do work wonders in our little circle. I only have so many terrors, when they're all in someone else's decks then there's a local short supply of anti-creature, and those unprotected big, bad, beatdown boys stay in play longer.
But trading them for cards you can use is probably more productive in your case.