I just watched the Despecialized Version, and it was a great great pleasure... It looks beautiful, and most of the times the jumps from version to version are not even recognisable. Also, your work with the mattpaintings shines through and I see the effort in making the transitions as smooth as possible.
Basically, this is The Empire Strikes Back, how it is supposed to be, in a quality that makes the GOUT DVDs something of a bad nightmare...
My beamer only works at 720p, so I can't tell, if there is much loss from the 1080p versions. The picture is sometimes a bit on the soft side (also the special edition material), but overall you're decision to render in 720p seems to be right for the material, since the jumps in quality are not as big.
My only two nitpicks are more about the color correction, which is as far as I know based on Adywans version anyway: 1. Is the always discussed blue Hoth.. the problem with blue taken out of the picture shows in some shots, were the shadows of Tauntaun and Han Solo appear blue, while the background is neutral. So for my taste it's too much corrected into neutral for that kind of material. 2. The lightsabers.. everyone is so concerned about them being bright and white, that those scenes suffer in picture quality, and so the overblown "shine", doesn't look very nice. But I know, it's a compromise between having them wrong or bright..
Anyway, I am very thankful for giving us back the experience of the original Version in HD quality and am very looking foreward to your future projects!