Harmy, the second link you provided in Japanese is the best quality version I've seen tonight. The color sure is awful, but I wonder how fixable certain portions are. The workprint on Return of the Ewok and the Star Tours documentary are simply unusable.
I must confess, it's always been a slight annoyance that ANH uses the exact same shot of the entrance to the trench. If Star Tours footage were fixed up, I wonder if it would be usable is somebody's edit (not likely Adywan's considering we'll never get the video quality he's seeking). Just an interesting thought, as the footage is similar enough to pass as the same trench run, but distinct as well.
As for ROTJ, I think a couple seconds skimming the Death Star surface could be useful. Perhaps portions of the trench run could serve some other minor plot point, like taking out some shield generator protecting the entrance or something. I don't know...also the shots of the Star Destroyers, particularly the closeup of the hangar might be worthwhile.
Do the experts know how possible it is to clean up portions of the footage and upscale as much as possible?
Too bad even finding a decent bootleg of Star Tours 2 would bring down the immediate wrath of LFL. However, I wonder if they'd mind if some borrowing took place from their advertisements.
http://www.youtube.com/watch?v=H2gc349FU9A&feature=related
It even has a shot of the Death Star II. I wish we were able to see more of that and even make use of it.