SilverWook said:
Was HFR even a thing in the late 80's early 90's?
There must be some arcane technical reason for shooting the models at 30fps.
As all of TNG was edited on NTSC video, any PAL conversion at the time was going to be problematic.
In the early 50s, Todd AO was created, which was a 70mm format filmed and projected at 30 fps. There were actually two films shot side by side with regular 24fps cameras and 30 fps Todd AO cameras: Oklahoma! and Around the World in 80 Days.
http://en.wikipedia.org/wiki/Todd-AO
Douglas Trumbull created his "Showscan" format in the late 70s/early 80s which projected 70mm film at 60 frames per second. No films were ever filmed in the format for reasons one can probably understand.
http://en.wikipedia.org/wiki/Showscan
As far as to why half the model shots were done in 30 fps, it just seemed like Dan Curry's preferred method. Rob Legato did every other episode's effects in 24 fps so there wasn't a real technical issue.