"a "car stereo" simulator - that's the one simulated space that seems a no-brainer"

I would disagree with that. Once you start simulating a car it becomes *which* car dilemma (and exponential variables).
Honda with Alpine? Cruze with stock? LE or EX model?? (could be different radio and speaker specs)

I wouldn't want to touch it. Not only are you trying to simulate speaker response you'd be trying to emulate environment. And making an 8X8 room sound like a car interior would be much different than a 12X16 room, and much different than headphones .. nope, not so easy as it sounds at first.
Just my thoughts/opinion.

I do not work here, but the benefits are still awesome
Make your sound your own!