The Excelsior (various sources describe it at 6' long) was maybe a foot or two shorter than the refit model (described as 7-8'). It WAS lighter, though. The Enterprise was a lot heavier though, because it was built with an arc-welded aluminum frame, and its pearlescent paintjob wasn't intended for shooting on bluescreen, which is why ILM dulled it down so much.
The refit Enterprise miniature was truly a work of art and a thing of beauty. The fact that ILM either couldn't figure out how it was intended to be shot, or didn't want to adapt to shooting it as intended, says something to me about the reputed "best in the business" effects house.