Snow White, BatB and TLK are all "Platinum Collection" which was originally the extra-special 10 Disney Titles, while the rest would be in the "Gold Collection", but Disney seems to have ditched the "Gold Collection" all together. "Sleeping Beauty" was not a Platinum title, but the Special Edition version seems to be constructed similarly to a Platinum title. The next platinum one will be Aladdin, I think.
I don't think there's a real difference between "Collector's" "Special" and "Platinum" editions - except Pixar movies aren't real "Disney" movies - so they get called something different. If you've seen the "Collector's" Editions of A Bug's Life and Monsters Inc. you know you won't get ripped off if you buy it now - there is very little they could put in a future release of the move.
As for Lilo & Stitch, if don't have it already, wait for the Collector's edition - but if you don 't need the extras, then I'm sure there's no big reason to "upgrade" your title - the transfer is top quality and I doubt Disney will do anything to improve the quality of the actual film. It might be nice to see if they include the "pre-9/11" ending of the film, but other than that, it seems like all the behind the scenes material on collector's versions of titles are all very similar, and if you're not really into the particular concept art, there's little to learn from those 2nd discs.
I for one won't be upgrading. Though I will be upgrading any of my old titles (like from the Special Editions that they release in the VERY beginning) that are widescreen titles to Anamorphic versions as they are released... so I won't be buying Alice in Wonderland, but I will be buying Pocahontas, Lady and the Tramp, Mulan, and Hercules when they come out with anamorphic titles. I'm also holding off on buying some titles I want, like Hunchback of Notre Dame which i heard has a pretty bad transfer. Since it's reportedly Eisner's favorite movie, it will probably get a better DVD sometime soon. 10th Anniversary coming up pretty fast for that one, actually.