I use a combination of Vality's Balmora Mod, PS' Balmora Ghetto, and http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=6051 (but make sure you clean that last one, if you do use it--dirty refs ahoy) myself. The three actually blend very nicely together; no conflicts at all.
I've never noticed an FPS drain with Vality's mod--possibly there's a minor one. I do have a pretty fancy whiz-bang computer so far as Morrowind is concerned, though, so I'm probably not the best judge on that front. It's definitely got a much, much lower impact than Balmora Expanded, though. And now that I think of it I was able to run it on my old laptop without much of an FPS hit, too.
Here's some screenshots from my Balmora:
http://tyraarane.riumplus.com/gallery/d/1777-1/Balmora1.jpg
http://tyraarane.riumplus.com/gallery/d/1782-1/Balmora2.jpg
http://tyraarane.riumplus.com/gallery/d/1787-1/Balmora3.jpg
http://tyraarane.riumplus.com/gallery/d/1792-1/Balmora4.jpg
http://tyraarane.riumplus.com/gallery/d/1797-1/Balmora5.jpg
(The fountains, ovens, etc. are from NoM--everything else is from the three Balmora mods and various texture mods.)