Something just occurred to me as I was reading an article about backwards compatibility in the next console generation (or lack thereof). I have close to 400 games and I really don't know why. I've been playing console games since the days of the Atari 2600. I still have every console and game I've ever purchased (except the Atari, ironically).
-NES -SNES -Genesis -N64 -Gamecube -Dreamcast -Game Boy Color -Game Boy Advance/SP -Nintendo DS -Playstation -PS2 -PS3 -Xbox -360
Now, I know I am not special. Probably half the people on Gamefaqs have a similar or larger collection. Thing is, why? At no point in the foreseeable future am I going to break out my NES and replay Operation Wolf, and yet I can't even entertain the idea of throwing it away.
It's a collection. If you're attached to it, keep it.
I've questioned whether I ought to keep my PS2 collection now that it is basically obsolete, but I like having those games and it's not like they're taking up a ton of space. And as you said, if you sell it the returns won't really be worth much.
I have well over 400 games myself and 200 of which are just NES games alone. If collecting isn't your thing then let them go so that people that do enjoy collecting can get your copies. There is a market for every game despite how bad it is or how unpopular it is. There are people like myself going for a complete collection that will buy every game for a specific platform despite their quality.