Actually, what about normal rooms not having spawners, instead spawning monsters (away from where you entered) whenever you enter a chunk that you haven't visited in a while, but they don't keep respawning right into your face.
Whereas bossrooms do have spawners, which get destroyed when the boss dies?
That'd be the more diablo-ey approach I've sene mentioned elsewhere on the forums.
And that'd give killing the normal mobs -some- point as well, as they'd at least leave you alone for a while.
Not sure if that might make things too easy, though. Hmm.