Well, yes, obviously the bigger the model the more convincing you can make it look...assuming you have a stage big enough to handle such a thing!
How the heck do you do motion-control work for a thirty-foot miniature? Heck, at that size you'd probably have to mount it upside-down to keep the pylons and dorsal strut from sagging, like they did with the 6-foot ILM-built E-D. I could see building certain sections of it in a larger size and using them for close-ups in the drydock flyby or the airlock and "wing walk" sequences, but I think they actually did that with the side airlock for the travel pod, and of course the personnel locks were built full-scale. But I like it that the flyby sequence was achieved by shooting something real and complete, that there are actual photos of the miniature surrounded by the drydock and the cameras just moved around it and documented it as it was (well, with the space background and other stuff added later). That's just so cool. And really, I think the refit miniature was the world record holder for a while as the most detailed ship miniature ever made. So they did pretty well at the size they used. (And I can't remember how big it was.)
100 inches to represent 1000 ft of ship. That was Richard Taylor's call, that scale, and the stated reason for discarding the mostly finished PHASE II model. The EVENT HORIZON miniature was 30 ft long and shot mo-con. That's bigger even than the MISSION TO MARS and SUPERNOVA ships by a goodly margin, probably 10 ft longer. I saw the M2M ship up close and was surprised that it didn't look as good as it did on film (as opposed to the E-E, which looked great even without the lights on, and the PHOENIX, which was like the most beautiful foil covered jewel you could imagine, especially with the nacelle caps.) I don't know that Trumbull would have built the whole thing at his preferred scale or not (even though that seems to be the inference, because he mentions the SILENT RUNNING VALLEY FORGE was 26 ft long.) I could easily see building a really huge midships partial, where you' have the top of engineering, the struts going up toward the nacelles, the main strut and a hunk of the underside of the dish. That would have allowed for the kind of shot I've always dreamt of, where you could do a tilt up from engineering to the dish that went through at least 150 degrees of tilt, which would be enough to get you dizzy if you shot it right, and provide immense sense of scale (which is a real toughie given the smooth-skinedness of the thing.)
Also, the flyover portion of V'ger was like 60 ft. long, but they obviously never zipped over it in a single shot.
^Well, just flying over a static miniature is easy enough. I was thinking more about how Enterprise model shots were generally given motion through a combination of moving the camera toward/around the ship and rotating the ship on its mount. The bigger the model, the less "maneuverable" it is. Not to mention that something like the Valley Forge, which was kind of a flat, linear design, would be better balanced than a top-heavy, connected-modules shape like the Enterprise.
Actually, they never moved the large refit ship on its mount in TMP because all the spotlights would not follow, since they were reflections off small dental mirrors. I think even when it comes out of drydock they're moving the dock, not the ship.