I don't know if it's all doors, but I've ran into a number of them that look like something my old 386 vomited out. It's all the more striking, I suppose, after installing so many graphic upgrades. You run across something untouched, and you feel like you just stepped in something unpleasant.

At Shenks (?) Shovel in Caldera, the interior doors are more low-bitrate than anything I've ever seen in the game. Don't know if this is original to the game, or if one of the upgrades I installed did it. I know the big Visual Pack reworked most everything in outdoor areas; did it do anything for the interiors of buildings? Is there anything that does rework building interiors--not just cups and plates and silverware, but walls, floors, ceilings, and doors?

Connary and Mr. Swiveller, among others, have full texture replacers for all interiors.
But, yes, there are a few doors that seem to have been missed by all but a few people, so you have to mix and match.
http://www.gamesas.com/index.php?/topic/1066048-door-textures/page__p__15488263__fromsearch__1&#entry15488263 for suggestions.

Thanks. So, are people using Connary's work instead of the Morrowind Visual Pack Combined?

Use whatever textures you like best.
Most of use a combination of many people's work.
Neither Connary or the Visual Pack covers everything, so you can use both over-lapping each other, and combined with anything else you like.