Oh, sorry, i didn't see that, though I searched for something like that in your post.
Since I do not know the mod I can only speculate, but as you describe it it seems to be a resolution-enhancemnt only, without adding more detailed textures. That doesn't sseem to be sufficient in that case, may be.
By the way, Doom and much more Heretic look still very good today, if you only increase resolution even without new textures. Since System Shock uses the Underworld engine it would be interesting to hear if Ultima Underworld has similar problems as you see them with System Shock?