The thing is though, Matt, that a lot of those re-releases you quoted are of movies that were originally released several years ago, with inferior transfers, flat audio, and weak features.
Certainly not all are, but for every "new" special edition released just to cash in on a theatrical sequel (I'm looking at you, Bourne Identity: Explosive Extended Edition), there's a new edition of a movie that really needed it--the new Goodfellas disc, due in August, is a terrific example. The old disc sucked--you had to flip it in the middle of the film, I don't believe it was anamorphic, and whatever the extra features were--I'm sure they pale in comparision to what the new one is gonna have.
A lot of those discs being re-released--their old versions were released in DVD's infancy, and were pretty much just laserdiscs transferred to DVD. The entire technology has improved since then.
In terms of what people do with their old discs--I think a lot of people use Ebay or Half.com. Some people just trade them into their local used record stores or pawn shops or whatever. As for me, I typically just trade mine to Scott for whatever Star Wars figures I either missed out on last year, or am too lazy to go search for this year. . .
