Overall though, I do not know if JEDI can be saved from its overall tone of silliness. Having watched it recently (and comparing it to A NEW HOPE and EMPIRE), it is obvious that Lucas' wife played a major factor in his life when it came to grounding the stories (they divorced some time during EMPIRE's production, maybe even right before). JEDI is just plain silly and illogical even for STAR WARS:
(1) they have a stolen Imperial shuttle and code, and even fly by the Executor (which then allows Vader to pick up Luke). When Vader arrives to tell the Emperor, the Emperor responds that he already knows what is happening - the rebels are in the shuttle. Yet the rebels land the shuttle somewhere in the forest, as if the Executor crew and the rest of the Imperial forces wouldn't see this shuttle land in the forest and not on the landing pad. I have to wonder why Lucas just didn't copy the basic jist of WHERE EAGLES DARE and just have them wearing Imperial officer uniforms and infiltrate from within.
(2) regardless, they encounter something along the lines of 8 scout troopers (whose outfits are designed for the specific purpose of scouting, such as the inclusion of BLINDERS), none of which simply turn on the radio and send a signal to warn anyone. As a result, they all die in somewhat spectacular ways while zipping through a forest at 100+ MPH.
(3) the Ewoks: maybe if they had sharp teeth (ala piranha) and claws, or as someone suggested, a somewhat "cannibal" vibe (maybe heads on pikes - again to bring over APOCALYPSE NOW motifs), I could believe they "could" possibly win in a fight with the supposedly "best trained garrison" in the Empire.
(4) the overall space battle: are those rebel transports (which do not carry any weapons) in the battle? Why is it that no rebel ship is destroyed, short of those hit with the Death Star laser cannon?
So here are my suggestions, just to throw them out there:
JABBA'S PALACE:
(1) Boba Fett: as mentioned earlier, either remove him or do something to give him a more fitting exit (ala the SW:HOLIDAY SPECIAL ending).
(2) I like the idea of making Jabba's palace more menacing with the altering of the doorbot (keeping the original "voice", maybe adding the scan lasers, even if it is a quick scan), the replacing of LAPTI-NEK and/or JEDI ROCKS with something more sleazy yet tuneful.
(3) remove Luke sticking his hand out to do the force choke on the Gomorrian Guards. Vader never had to point to his victims to use his power, and it would imply that Luke had indeed expanded on his training and power in the time between EMPIRE and JEDI.
(4) The idea of someone shooting at Luke when he reaches the door in the Rancor pit (or add electrical effects to show the door being electrified - in fact, maybe have Luke using his force powers to try to open the door and Luke gets zapped from a Jedi-made trap created by Jabba).
(5) maybe have the door come down harder/faster on the Rancor and do something to show/imply Luke using his force powers to bring the door down with enough force to crush the Rancor's neck.
(6) make the "sails" on the sail barges bigger, as well as maybe adding some sails to the vehicle Luke and Han are on.
(7) removing the "force kick" or bringing the guard closer, as well as straightening out the kick so it looks more like a martial artist as opposed to a beginner.
(8) I vote to retain the original Sarlaac sans Audrey beak, as well as possibly make the Sarlaac bigger and with more tentacles. Anything to make it more frightening and threatening would be good.
ENDOR:
(1) I think the ringed planet in the sky would be a nice touch, as well as the added morning effects - anything to show a passage of time in different parts of the day.
(2) Ewoks: again, anything that can be done to tone down the non-threatening nature of them, or anything that could be added to improve their threat level.
(3) I agree with an earlier post to snazz up the 3PO "flying chair" scene to include thunder or other sound effects - maybe have the fire/torches change color as well.
(4) maybe decrease the number of Scout Troopers the rebels contact - it is hard to believe that not ONE of them gets a message off or actually does their job and warn the rest of the garrison.
(5) this may be impossible, but is there any way to imply that some of the troopers and/or officers are rebel spies that have already infiltrated the shield generator? Even if it meant taking dialogue from WHERE EAGLES DARE or other WW2 movies and having it said "off camera" (say in the briefing scene) to suggest there are people already waiting to meet up with Luke and co.
(6) snazz up the AT-STs: make their cockpits more like the AT-ATs by replacing the cheap-looking "pop-up" windows with a single glass window ala the AT-AT cockpit.
(7) improve the explosions/destruction of said AT-STs: longer explosions with more debris - anything to indicate they are more than just models.
(8) when the Ewoks attack, maybe ditch the more goofy traps and replace them with something simpler, like pits the AT-STs or stormtroopers fall into. The inclusion of "body parts (forearms and/or legs)" being thrown into the air when the stormtroopers are ganged up on as well - nothing too bloody but an indication that the Ewoks are just as strong as Wookies despite their size.
(9) again, don't know if it could be done, but could even SOME of the stormtroopers be shown to have camoflauge (a slight jungle camoflauge layer over the white armor)? I mean, they ARE in a jungle and all. Or put in another way: wearing white in a starship with grey or white corridors, as well as white armor when fighting in the snow kind of makes sense. Even wearing white on a desert planet wouldn't be as bad as in a jungle.
(10) PLEASE get rid the stormtroopers and Imperial officers constantly saying FREEZE, especailly when they are at war and the Empire does not take prisoners (unless ordered to by choke-happy Vader). I do not know how to get around some of these scenes (like Han and Leia at the front door) but Jesus Christ on a tap-dancing pogo stick...
THE EMPEROR'S THRONE ROOM:
(1) I do not know if anything can be done, but the throne room is rather cheap looking - a lot of "girderesque" construction ala the BALCK HOLE sets.
(2) something has to be done to justify Luke defeating Vader. JEDI could not be more than 2 to 3 years after EMPIRE, unless there is a good deal of time that passes between rescuing Han and the rest of the movie. Thus, how would Vader go from the strength and power he had in EMPIRE to in essense just "giving it up" and allowing Luke to beat him in the final fight? Could we have a reflection of the Bespin fight by showing Luke ripping off pieces of equipment and hurling them at Vader as Luke beats him back towards the elevator walkway? You could play the scene "as-is" but just add a tornado of machinery and chunks of metal swirling around and being thrown at Vader as Luke simultaneously fights him with his lightsabre.
(3) should anything be done to the Emperor's "tower" - as in make it more of a temple ala the BLADE RUNNER building on the surface of the Death Star, as opposed to a tower that would be easy to destroy by a starship?
THE SPACE BATTLE:
(1) add more larger rebel battle cruisers and take out the freighters and transports - unless they are shown to "kamikaze" into Star Destroyers and/or the Executor.
(2) the mass of the Imperial fighter fleet needs to be addressed, as well as show the Imperial fighters actually taking out rebel ships - when watching JEDI, it always seemed that the Falcon was destroying everything and the Imperials weren't doing anything.
(3) the Star Destoyers need to be shown firing a LOT. While I may not suggest copying the camera work of this scene, the space battle finale in SERENITY would be a good reference point as far as capturing the chaos of a large space battle (minus the camera zooming in and out of focus).
(4) when the Death Star fires, show the beam making a "right to left" raking motion, as well as show multiple rebel ships taken out with the laser swipe. Of course, add better explosions and debris (maybe large chunks of the ship flying or spinning off).
(5) the Executor: I would rather show something to the effect of multiple rebel transports kamikazii-ing into the Executor, or having multiple rebel ships firing upon it than to see this large ship get taken out by a single fighter flying the length of the ship's hull.
(6) I am on the fence with Lando's possible death: I love the "skin of the teeth" escape, but Han's line about not seeing the Falcon again needs to be dealt with (either validate or remove).
THE END:
(1) personally, I would stick with the original NUB-NUB song for no other reason than there would be no celebration across the universe (yet) as it would take time for word to get out and you still had the rest of the Empire to deal with (other Gran Moffs, etc). If anything, the rebellion's work would just be beginning - case in point: the end of the WHITE MOUNTAIN series. After the "Masters" are defeated, the rebels essentially start to bicker over who will be the leaders of the world and start to verbally fight with one another (as the leader of the rebellion puts his head into his hands). The main characters realize that they won't be "sailing around the world" or otherwise enjoying their new-fouind freedom, but have to continue the fight albeit in a much more boring way. To celebrate the end of the EMPEROR is one thing; to pretend as if their work is done is pretty preposterous, unless:
(2) you add in Piett or another imperial officer shaking hands with the rebel leader to indicate that a peace (and thus a new republic) is being formed, thus a real reason for the citizens of the "Empire" to celebrate.