Unfortunately most game models have already been optimized as far as they can go without leaving holes in the model, that's part of the artist's job.
To get models for conversion that won't tax the system (for Trek) you'll probably have to go back to Armada I and earlier.
I hate to say it, because I love this game, but the 3d engine in SEV is woefully behind the times and underpowered. Then again, 3d is not what the game is all about!
