I don't know if anything could really be done with this, but it occurred to me that there might be something to be done with Boba Fett. I'm not exactly sure what, but at least consider that there are a few brief seconds in Return of the Ewok where we see Boba aboard the Death Star II, and that those brief seconds happen to be higher quality than the rest of the film. Perhaps there is some slight subplot that could be worked around his presence there. Again, it would require some serious fixing of a low-quality video source, and I don't know what else could be done beyond that, but perhaps you guys can think of something.
Around the halfway point is Mr. Fett. Again, I don't know if it's salvageable, but if so, perhaps further special effects (e.g. removing Wicket) and a plot can go with it.