They put a new team on it and had them produce improved models/FX for the following seasons.
That's incorrect. Same team (CBS Digital), they just learned from their weekly grind how to improve their rendering speed and CG modeling skills.
The new Enteprise CG model was debuted after a handful of episodes were made (8 to be exact), not an entire season. It debuted with the airing of "The Trouble With Tribbles" on the week of November 4, 2006.
Also note, TOS-R was done in batches grouped by "popularity" for first run broadcast syndication on US TV over the course of 2006-2008, not in the original production order. So those 8 episodes with the pretty poor Enterprise model is in a few second season episodes they did in the first 8 as well.
The eight episodes with the rather poor Enterprise model are (in 2006 TOS-R airing order, not original order):
Balance of Terror, Miri, The Devil in the Dark, The Naked Time, The City on the Edge of Forever, I, Mudd, Arena, Catspaw
The subtle changes to the live action footage with the actors are almost all terrific and seamless (stuff like Scotty's phaser beam in "The Naked Time," Sulu's clock in the same episode, matte extensions, etc.). The new model shots, done with CGI, are much more of a mixed bag.
I find the new cityscape and structure shots almost invariably to be superior to the originals.
Yes indeed. The work Max Gabl and others like Niel Wray did on enhancing planets and planetscapes (matte paintings) is incredible work and very faithful to the original work. Those same guys are why the new TNG remastered planets look so great