MOST of the vfx elements were shot on 35mm, but by no means all of them.
This means then that they have a large archive of FX material that they could use instead of redoing everything. Now the question is, how feasible would that be?
[no relation to screen name...] Even if TPTB were to do a TNG-R they would have to reconform all of the 35mm original camera negative of the live action stuff first.
If they were to try to pull the 35mm visual FX material (model shots) it would be a lot more work plus they would have to telecine shots and then do new CGI visual effects and then composite it.
I've said before
on this other thread:
models built for the TNG feature films but sticking to this thread if they remaster ST:TNG and recreate all of the ship shots and visual effects I can assure you it is easier for them to do ALL of them in CGI for consistency. The animators could just refer to the original show for camera angle and ship movement.
Even if they could locate the original camera negative of the 6ft. ship model for each shot and telecine to HD and then adding the CGI stars and phasers anyway would negate using the film source to do it in a timely manner.
Multiple CGI models have been built of the Enterprise-D already.
This post discusses them
and has pictures. This post
has additional info without pictures.
If a TNG-R were to be done it is just much simpler
to do all space exteriors in CGI. For the purists they can watch the original visual effects done with models mostly (in 480i standard def. unconverted to 1080P HD) with some branching feature on the Blu-ray.