Somehow I suspect someone could reedit Schumacher's awful Phantom of the Opera film to replace their non-singer Phantom with Michael Crawford's voice (and other voices from the original soundtrack) wherever possible, and remove the "sideshow boy" flashback. That would be neat. Emmy Rossum and her lowcut dresses can stay though. =)
(This is sounding like a better and better idea to me. Some creative editing could fix some of Schumacher's more uninspired camera angles and lighting - if a closer shot is needed on a too-wide shot, one could grab the pan & scan version and letterbox that, to get a closer take ... chromakey and filters could make any colored lighting more subtle ...)
How about Almost Famous with extended musical sequences including some form of "Small Time Blues?" ("Small Time Blues" was the inspiration for the "Angel Town" sequence in my film Gods of Los Angeles.)
The Masters of the Universe movie would be a fun reedit - it would still suck, but one could reedit it to be more like an episode of the TV series. You could make it short ...
Oh! At one point I had considered doing an edit of Monty Python's The Meaning of Life - reinstating the cut scenes from the DVD, moving The Crimson Permanent Assurance back into the movie at the right point, and reinstating cut/changed lines heard on the soundtrack album ("Well, it's sort of a link." "Ooh, have a nice month.")
Oh! This would be weird and kind of pointless, but how about an edit of The Nightmare Before Christmas which uses the opening/closing narration (Patrick Stewart) from the soundtrack album, maybe a couple of cut shots from the DVD if they're worth it (but there's not much to speak of), and maybe even have someone animate (via CGI, but to look like cutout silhouettes) the cut "Oogie's Dance" segment heard on the soundtrack and discussed in the book.
That would be pointless, wouldn't it ...
Easy dumb obvious one - Extended Sin City. Cut back into one movie, a la the theatrical cut, but with the extra scenes of Hartigan's wife and Mort and the Nurse put AFTER the appearance by Senator Roark, where they'll make about ten times more sense.
In my "impossible dream edit" category:
Terry Gilliam claims that his second-to-last cut of The Adventures of Baron Munchausen (running 12 minutes longer) was much better than what was released, because it had a more natural pace and "breathing room." This cut is long since lost. The Criterion DVD didn't turn up much deleted footage ... most notable was a better extended cameo for Gilliam himself.
The deleted host segments from MST3K: The Movie have turned up somewhere, haven't they? Probably a terrible cam bootleg from one of the conventions.