As for rennervision, I was going for actual changes that could be made to the OT in a future release. However, I'm totally with your suggestions, as RotJ is unquestionably the weakest of the first three films. I would, to name a few:
-Handle the completion of Luke's training better. He should have gone back to Dagobah at the end of ESB, so open JEDI with Luke's final trials from Yoda, who has grown old and weak, and have Luke leave with his death. The only problem with all this would be Luke getting the true story on Vader from Ben and Yoda. Surely the topic would have been brought up in the years between the films, so where does that leave the big explanation scenes? Something to think about...
-Make it clear in RotS that the Empire was builing two Death Stars at once. This would make everything much more plausable to me then rolling out yet another superweapon with the same basic weaknesses just a few years later.
-Furthermore, I'd have the DS2 being constructed over Kayshhk (or however you spell it), using Wookies as slave labor, thereby replacing Endor and the Ewoks.
-Tranplant the excellent Luke/Vader/Palpatine scenes to Coruscant, possibly to the volcanic Sith Catacombs.
-Have the Rebels attempts to destroy the DS2 fail. However, Luke, at his peak of clarity after defeating Vader and denying Palpatine, reaching out with the Force and destroying it himself. (I must admit I didn't come up with that myself, I think I read it on T'Bone's site somewhere in an feature on improving RotJ.)