Except some of the sets for the TMP enterprise wouldn't actually fit inside of the model at the scale it was originally designed. Engineering is by far the biggest perpetrator; the engine room sports several perpendicular corridors that lead to places that couldn't exist in a hull that size and would only be possible if the ship itself was nearly twice as large as originally designed. Abrams' people evidently encountered the same problem with the filming sets when they realized that there was just no way they could justify cramming something that huge into an engineering section only forty meters wide; especially once they decided to do it big with the (IMO, totally awesome) airport-sized shuttlebay. Try to remember that the majority of spaceship effects and exterior CG are mainly done in post-production after most principal photography is completed. If they finish those CG shots early, it's usually for the purpose of sticking it in a preview.