I wouldn't say they were copy and paste. The big recurring themes in an advanced civilization is planned cities. Thus one could argue that the Ayleid ruins are just planned cities that used similar aspects. People have to get over the "copy and paste" aspect of the dungeons, EVERYONE DOES IT!!!! It cuts down on production time to use prefabricated sections and rearrange them in unique ways. Technically, not one ruin in Oblivion was the same. It's not like Bethesda is lazy, everyone that has to make dungeons on a large scale uses several areas multiple times. I for one thought the Ayleid ruins were wonderous. Also, most of the Ayleid entrances are unique, several of them were beautiful, with statues of different beings and ruins of what would've been beautiful architecture.
Comes down to creatively making each dungeon unique though, which also depends a lot on the set of models you have available. Even if each dungeon is unique, if they all share the same elements, like a long hallway with traps, that leads to a large room with treasure, but this one bends right while that one bends left, they tend to feel the same. I'm not saying I thought they were all the same, but I do wish they had added something creative and unique to each dungeon, like a room or areas that you could specifically recognize as belong to that dungeon and only that dungeon.
Whenever I would make interiors in the Morrowind Construction Set, especially for a dungeon, that was my goal, find something that would make this dungeon unique, by using pieces in unconventional ways(however, then the player shouldn't be able to spot that you are doing that) or adding a "background story" to it by items you place. Even if it was a small insignificant dungeon I could usually find something to make it interesting.
I thought a lot of the dungeons were interesting, but then some certainly seemed to just be plain repeats of others. It was hit or miss IMO.
Somehow I think "These guys" will be "The current, living races who we are familiar with and not some totally random other group of people whom it would not make sense to refer to so casually".
I imagined bandits. I don't really see the Nords turning them into viable settlements. I'm thinking the Dwemer ruins is basically just shelter now for whoever finds them convenient.