I've been doing a bit of experimentation using diffusing filters to homogenize the light source and reduce the led die hotspot in an aspheric setup.
This image from Edmund optics got me headed down this path. I posted a question regarding holographic diffusers last week, but it ended up with no bites so I presume it's either something that will prove impractical in the end or it's just something that nobody has really messed around with much yet.
In as much as this might apply to incandescent setups, I only know how basic projector design works.
Now, ALL CAVEATS: I have no idea how the reflector/bulb/lens system performs in reality. Dave notes that less than a sixth of the light will make it to the lens in the first place without a reflector, and you would need a rather unique reflector system in place to make the focal length of the reflector match the focal length of the lens.
MAYHEM!
Using LEDs has been much more straightforward for me, though I have yet to figure out just how many lumens I am missing out on due to not having things optimally configured.
I hope I'm not spewing lies at this point.
I'm a tinkerer at the moment, using my computer science background to pretend I'm an engineer. At any rate, good luck with things. Let us know if you continue down the incan + aspheric path. Could be some neat experiments if nothing else.