-The voice of Grievous: I wouldn't make it TOO different between I and III. The audio is going to be an important connection between the character in I and the character in III, as the visuals are different enough.
-Cutting C-3PO from the film: Tempting, and quite easy to accomplish. But then we have the problem of II and his relation to Anakin. No, I think 3PO in I is a necessary evil so to speak. Without it things would get even more confusing. Though I wish Lucas would release the original footage of him in his skeletal form in II, and the scenes with Padme completing him. Who know's if they's be of any use to us or not, but it would be interesting to see regardless. Question: Your last statement made me think in your edit you've made it to where Anakin did not build C-3PO. Is that the case? If so then my eariler argument against cutting him from I is void and he should be edited out immediately!
-Episode III: This will all depend on who will be doing how much on the project, and we can deal with that when the time comes. I definitely think bringing out the Obi-Wan/Padme suspicions of Anakin would be a good move. Once again, I wish Lucas would have released the scene of Obi-Wan visiting Padme to discuss his worries over Anakin. It would have been a good character building scene, and Anakin even senses his presence there later in the film. I'm looking forward to seeing your ideas about Qui-Gon interfering in Anakin's nightmares as well. As for everything else, what do you think of the removal of "Darth" as a title?
Btw, I really liked your suggestion of placing Peter Cushing next to Palpatine in the Senate. That hadn't even crossed my mind but would be an excellent addition. Hopefully we can find more special effects people to assist us with those types of shots.