Thanks AntcuFaalb, that link was a good read. I hadn't considered much that Lucas' old transfer would be lacking enough that 720p doesn't make all that huge of a difference. Makes me somehow feel incredibly better about this whole project knowing there's not much in the way of quality loss (every single edit Harmy's made is nothing other than a benefit, but quality difference had been a concern in the back of my mind).
Not to say that there isn't a difference between good 1080 and 720. *sigh* Damn you Lucas...