I can see why some would want the Holiday Special on a good quality transfer. It is a part of the Star Wars history.
However, I never really knew how much THX had been changed. Saw the original on TCM when I was a kid and it completely blew me away. I knew some changes and CGI had been added in for the DVD, but it was supposedly seamless when compared with the original version and has been lauded.Here is a link to the only place that has done a comparison of the two versions:
http://www.maverick-media.co.uk/movies/thx_1138_1971/changes_001.html
After proudly owning the DVD for a couple of years-I now realize that it is completely different from the film I thought it was. That hurts. Ironically, GL's most profound and philosophical statement has been truncated by none other than himself.