The somewhat disturbing issue with going to HD resolution for TNG is that the imperfections of the production will stick out much more obviously. The models and sets for example were definitely not intended for that kind of clarity.
It's almost going to be worse than TOS in a way in my opinion because TOS was very obviously simplistic and was leaving a lot to your imagination in general, but TNG tried very hard to look convincing. All the paint chips and scratched metal panels in the hallways, the paint and decal oopsies on the props/models, all hidden by SDTV, will show super clear at 1920x1080!!
Hell, I started to notice this stuff just by going from my VHS recordings to the DVDs.