Hmmm
Consider requesting help from some demo coders (demo as in demoscene. not demo of a game) to assist you in optimizing the rendering code. These guys can do magic with little to no resources. This would lead to either better gfx without a performance hit and/or less stress on the cpu for the gfx which frees up cycles for the simulation.

Also, they could most probably make it look nicer which would widen the audience which is only a good thing for the LFS.

Just thought i'd mention it
Thanks guys, for everything.

I don't think the biggest CPU drain is the graphic engine (although it needs tweaked to make use of new cards), but more that it's calculating all of the physics objects in real-time.
Remember that your copy of LFS is calculating the physics of every car and object on the field (unlike most games that just update opponent positions), not just your own. I'd bet that's what eats CPU more than the rendering.

That said, I'd like to see what they could do with it.

physics code uses way more code than gfx rendering, but optimization is almost always welcome.
(i've done some opengl coding, reached shaders... and quit. )