But that only makes sense for the couple of scenes where the saucer actually separates. The 6 foot model's smooth surface was not unfinished at all, it was the designer's intent. It's details were incredibly fine and intricate. What you're confusing is the more exaggerated features of the 4 foot model for more detail. On TV screens (in the 1990s) the 6 footer's details don't come across as nicely, so the over-the-top 4 footer translates much more clearly. When you make the move to feature film that's no longer the case. Yes, this is common knowledge, but it has nothing to do with why the Excelsior model was built. The Excelsior model was built because the script for Star Trek III called for the ship to appear.