I don't know what the original source for the video is so their might be a less compressed version out there than the Rebellion Collection version.

The source used for the Rebellion bonus disc was the THX Ultimate Demo Disc DVD. Before that, THX WOW was part of a Laserdisc Demo that also included the featurette Soundtrack.

The version on the Ultimate Demo DVD was upscaled to 16x9 by Lucasfilm and is the same version on Rebellion. Unfortunately, compression issues between the two are just about the same :(

Also unfortunate is that the scenes featured in the demo are too short and incomplete to be of any use for most projects. I sent a 720p upscale of WOW to Harmy a while back for his Despecialized Edition, but don't think it was of any use to him.