All you really need to know about the PS WD variants is here

http://www.game-rave.com/psx/playsta...igns/index.htm

In regards to the Saturn and Sega CD stuff, I don't know how many are really all that much harder to get vs the other alternate arts save for the Sega CD Lunar SSC. That one was easy, the later the version, the rarer it was, with the 7th being the rarest.