Some things that came to my head:
Empire
1. Modify the Emperor's voice so he sounds more like in ROTJ.
2. Enhance Bossk a tad (like the Cantina creatures).
3. Have the voice in Bespin that says "Who are you?!" sounds more like a stormtrooper, so it makes sense 3PO goes "Stormtroopers? Here? We're in danger!".
4. Restore Darth Vader's "Ahhhgh!".
5. Have ligthnings below Luke when he is hanging for his life in Bespin, to make the possibility of his fall even more edgy and exxxxtreme.
Jedi
1. Have Jabba drooling foam when Leia strangles him, sort of a sick end for a sick character.
2. Fix bad music editing during the Sail Berge Assault.
3. Fix bad music editing when the Emperor arrives (maybe re-editing the scene so it matches with the Album version of the cue).
4. Fix bad music editing when Luke attacks the Emperor (this one lasts a few seconds though).
5. Fix bad music edits in general (ROTJ had too damn many).
6. Fix instances where Ewoks make Jawa sounds.