I pulled out my original Keep on the Borderlands and flipped through it for inspiration (read: ideas to mine for the upteenth time) and was struck by how much 'free space' there is in the map. Many rooms are separated by long, winding passageways. I like the breathing room of it... you can have a fight in one part of the dungeon, and there's a chance that no one in the next chamber over hears you, because they are hundreds of feet away around winding hallways.
A wolf or giant spider can wander in and roam around in your house, because it's not compact, and you have friends and allies on the other side of the complex, down a slope and around two corners. I can see the room for random encounters. Many modern designs (including most of my own) are so tightly-packed that there isn't any room for monsters to just roam around looking for adventurers to kill.
The other thought I have (in a similar vein) is how important it is to have multiple entry points to the dungeon. It's got to have a somewhat 'open floor plan' in order to facilitate some traffic flow that allows the environment to breathe.
As I said, just some musings...