Other materials are ok. I've already had trouble with them so I fixed all of them... except the emitter, which is not visible. Does the appearance of the emitter affect the scene? It's a matte material.
Also, does swapping the emitter for a area light do anything useful? (Sorry I ask a lot, but it takes such long times to see if these things have any effect.)
EDIT: Just noticed the default emission color for area light (this is luxblend25 under Blender 2.54, btw) is 0.8 0.8 0.8, so I've changed my emitter mesh accordingly. Keeping my fingers crossed. eff is up to ~1500%, as well, which sounds good, right?