I thought most, if not all, the ROTJ deleted scenes were in fact HD? My feeling about this sort of thing is that if you're going to put this much effort into something, you should try to make it at least somewhat future-proof. I mean, look at Adywan, he decided to stick with SD for ANH:R and he's already planning to redo it in HD.
To me, 720p is the best compromise, you get the resolution of an average 35mm print, so it should be presentable on pretty much any size of screen, and yet it isn't much more difficult to work with than SD even on slower hardware and you can upscale SD footage to 720p with reasonably good results. I believe these are the same reasons why Ady decided to go with 720p for his projects.
But it's of course completely up to you guys - your project, your rules :-)