I haven't seen enough of the series to make full-fledged suggestions in this thread (and I've actually been avoiding reading most of the comments in this thread to preserve some spoilers), but I have started to feel more and more strongly that a new PT could be constructed using TCW as Episode II. I've mentioned it before so I know this isn't knew, but I would love for others who are more intimately aware of the plots of TCW to contemplate how to complete such a trilogy. I think a few elements from Episode I plus most of Episode II could be pieced together to make a more interesting film, introducing and killing Maul early on, Anakin, Obi-wan, and Tyrannus/Dooku. Episode II could introduce Asohka (and eliminate her, though this is more difficult with the series' end), introduce Grievous, introduce and remove Ventress (another difficulty), develop Anakin, reintroduce Maul, and develop Dooku. It could also better develop the friendship between Anakin and Obi-wan. Episode III could then be an improvement on the current Episode III. I know it would be a drastic change, and while I think I've come to prefer TPM over the other two prequels, it really serves little story purpose and could go. Characters who were seriously underutilized (i.e. Dooku) or underdeveloped (i.e. Grievous) would appear more interesting by the time we got to ROTS. We would already see a Force competent, sympathetic, but dangerous Anakin. Maul could get the treatment he deserves. Sidious's goals with his expendable apprentices would appear more interesting. My only worry is that there would be so much to cram into the new Episode II that likely some of the most interesting elements would in reality have to go (likely Maul, maybe Ventress). I think it's worth consideration. I don't care about the change in visuals between films!
EDIT: Further thinking has led me to even wonder if the first trilogy were actually made into a quadrilogy. Obviously this would mess up the numbering of the later films, but if folks could deal with that, I think one could make an interesting set of prequels.