>>7
Doppler is cool. I am more fond of positional audio (psychoacoustic 3D panning essentially), but doppler effects come in second.
>>8-10
Ideally that will encompass everything I said above. I looked into it but never tried to implement it because I didn't think I'd be able get enough quality out of it to make it worthwhile.
There are two approaches, however. A cheap way seems to be to precompute filters for the entire geometry and ignore any moving obstructions (e.g. player) and forbid destructible environments. You can degrade the effect quality without ruining the sound quality. The effect might not sound great, but you won't get bursts of noise or whatever.
The ray tracing style approach needs realtime effect computation and when the effect quality degrades the sound quality goes with it.