Gerald Wallace, barring a return to his form of not one, not two, but three years ago, will never be an asset with positive trade value. This year he is a straight-up negative asset. Next offseason, he will also be one, but less so. Your best hope for trading him is if he has a renaissance season next year, at which point he might have mild value at the trade deadline.
Honestly, I like Crash. We're not doing anything better with his salary, so might as well keep him this year, and see what happens next year.