Personal ideas : Most elves should refuse to live underground, or sleep in a stone room. Only the most opposed to traditional ethics and values (some dwarves are like that, right?) could accept this.
Thus if we want elves we will have to keep a secured zone outside.
For humans, I think they could bear living underground but it should strongly reduce their morale. At least until something is done with lights. Enough light should prevent this.
In an other type of ideas, I think elves and dwarves should have different night visions (dwarves would be very efficient at seeing in the dark, allowing mining in completely dark places; elves can only discern shadows and movement much better than humans and dwarves).
Anyway I think it's a good idea to have real differences between races.
Seeing in darkness: dwarves>kobolds>goblins>elves>humans
As it is in-game currently dwarves=kobolds=gremlins=trolls>goblins>humans=elves. I remember one of Threetoe's stories having a plant that kobolds ate that gave them their night vision as well as their glowing eyes. Don't remember which one though. Anyway, I think I like the low light vision as it is, elves have no reason to be good at seeing in low light, while dwarves and kobolds are subterranean creatures, and goblins are kind of subterranean creatures.
I would think there would be different things each vision can make out, rather than a flat, dwarfs see better than elves who see better than humans. I would imagine dwarfs would be great at getting a sense for their surroundings underground, but be unable to make out any details like the engravings on a statue in complete darkness. Where as elves would better at distinguishing movement in the darkness but struggle to actually see anything or know whats around them, this would stem more from their hunter/cat like feel I attribute to them. Kobolds and goblins I am not sure how their dark vision might work, I could possible see koblods having the same general type as dwarfs, able to know whats around them but not to be able to distinguish details. I could also see kobolds having a limited form of extrasense that works off of smell so that they'd be able to tell one another apart in the dark. Goblins I could see them having human or elf types of dark vision but it would be supported by a keen sense of hearing that borders on echolocation, but not quite.
To recap my thoughts I see one type being Aware of your surroundings, such as knowing there is a drop off there and a wall there but not being able to see details or make out important details like is that a dwarf or a goblin. Dwarfs and Kobolds, would make use of this type with the kobolds have the additional ability to distinguish people based on smell.
Another type would be able to notice movement and reliably track it, but otherwise unable to know whats around them in the dark unless there is a light source. I attribute this to the elves given its something anything that hunts at night, but no underground would need.
The last Type I imagine would be used by goblins to make them stand out even more from your typical fantasy goblin, It would be based off a keen sense of hearing that would give a vague idea of surrounds such as distinguishing between a large cavern and a tunnel and being able to track things based off noise. Goblins might also compensate with the elves night-hunter vision that lets them track movement, but that would be redundant to their keen hearing.