Episode 3 had tons of footage cut. The original cut of the film had Anakin's fall revolving far more around seduction of the Dark Side and Palpatine's politics instead of the love story. They did a lot of pick-ups after the initial rough cut that emphasized the Love Story angle, this is why the two rebellion plot scenes were cut. That they are so complete indicates that the other missing scenes might also have been completed as well, but I doubt we'll ever know.
I'm a freak for Disney's much maligned The Black Hole. There are at least two deleted scenes that admittedly don't add a lot to the story but I'd love to have them regardless. But more impossibly, in the 'dream' realm I wish they had filmed and done post on the original ending they had dreamed up in which after entering the Black Hole, the surviving crew are scattered on a molecular level and turn up on Earth. The original concept had the camera spinning in on Kate's eye like the theatrical does, camera zooming closer and closer until it's just dots, and then pulls back in a sea of dots which then resolve into the fingertips of Michaelangelo's The Creation of Adam, then pan down to see Kate sitting at a pew. They hand't resolved if they were going to show all the surviving characters, or even what this ending was supposed to have meant, but they did go to the Vatican and filmed the needed shots.
Of course, the real problem was that ironically, for a story that focuses on what would happen if you entered a black hole, they didn't have an ending scripted even while filming.
edit: Oh, and regarding Galaxy Quest, the one way you can tell it had been planned to be raunchier is that if you pay attention to Sigourney Weaver's mouth in the scene just before the chompers, she clearly mouths "FUCK THAT!" but the line we hear is "SCREW THAT!"