Here are the comparison screenshots for the first and second 720p and the second 1080p. (the third 720p and the first 1080p were not that different from the rest. So I didn't include them in the comparison)

http://www.dacklinyoung.com/EXPORT_COMPARE.jpg

After your first 720p export, the compression seems to be making the same negative effect on each version. You can see in the first 720p how much detail was in C-3PO's chest plate and on his face. The compression in the other versions also gets rid of detail found in left hand corner of the frame.

What program did you use for the first export? Any idea what the settings were?

I'll be sending more notes and suggestions later today or tomorrow. This was all that I could put together for the moment.