You could never make the pre-THX sets look better or sound better than the THX ones, the noise floor is too high, the colour is all over the place the detail is very soft and the sound is awful - however certain scenes may be worth lifting to help deal with the temporal noise reduction on the THX sets.
That process was already underway before I left.
The difference in noise reduction between faces and definitive isn't much, both sets have their flaws and advantages over each other.

Most of the noise on the pre-THX sets is encoded into the disc unfortunately, so the X0 reproduces the encoded noise perfectly

The Special Collection may be worth a look, the discs mastered for the Japanese market tended to be of a better quality, so it is worth investigating. Karyudo might have the set, but I doubt it, I've never seen it for less than US$200, so most people gave it a miss.

When I left, the initial run of the X0 project was going to clean up physical film damage and laserdisc artifacts only, as any other version would need that done first.

Fixing mattes etc. was for after an archival version was laid down, so we did a lot of experimentation with removal of those, but there was to be an archival version that left them alone.

Of course that might have changed since