I'd say that if you're strapped for cash and that's the reason to "release" some of your gear, then an educated decision needs to made which to get rid off. If, on another hand, this is not about getting purchasing power for some other needed gear, then I'd definitely keep it. Barring some new "disastrous" new development in imaging technology (digital was one) I think the market has leveled out and, if anything, most gear will improve in value from now looking forward.