Wayne R. proposed in this blog post that Kobolds might be more interesting as "Dungeon Elementals" - creatures that exist only to reset dungeon traps, lock doors, clean up stuff, etc. Almost more of a Dungeon Maintenance Crew than the race of Draconic Megalomaniacs that they've evolved into.
Go read his article, it's really quite inspirational. I'm not going to repeat much, but instead I'll offer some thoughts of my own.
I love this idea. It clings to the sort of weird ecology that one might find in a universe where D&D things are possible. Kobolds are to Dungeons (specifically dungeons, not just caves) what Faeries are to Nature. The deepest, darkest Dungeons (as proposed in this blog entry) may touch the elemental plane of Earth, and may not even truly have been "built" so much as "grown". Maybe Kobolds are the Earth Elemental's way of maintaining and driving their creations once they've slipped into the Prime Material Plane. If you subscribe to the "Malicious Dungeon" concept, then Kobolds may be the agents of that malice, like electrons are to electrochemistry. Or conversely, once mortals build their dungeons deep enough, they inadvertently catch the attention of the lords of the plane of Earth, who send their material-plane allies to work the dungeon. Why? Who can fathom the will of Elemental Lords? ;)
In any case, Kobolds themselves are rarely encountered in person. They are exceedingly stealthy and can create secret passages as necessary to move around a dungeon undetected. As minions of the Elemental Lords, they seek to bring order to any dungeon they are charged with. They will coexist with other dungeon inhabitants, but in a Kobold-infested dungeon, even the monsters know to tread lightly. The Kobolds may not interact with them directly, but any denizen who causes too much conflict will find themselves on the wrong end of a trap, or locked in a room they could previously leave at will.
A Kobold infestation is a very serious threat to any mining operation, and many a delve has had to be abandoned after it reached too far into the ground.
So how do you get rid of a Kobold infestation? If you can trap them yourself, you'll find that they are physically unimpressive and easily slain. But hunting Kobolds is almost more like hunting Poltergeists, and their numbers are always more than you imagine them to be. Rumor has it that in order for an Earth Lord to send Kobolds, it must establish a gateway somewhere in the dungeon, and destroying this gateway is the only known way to end the Kobold threat. Once the connection to their Lord is lost, the Kobolds will gradually fade away, perhaps in search of another dungeon, perhaps re-absorbed by the very rock itself.