So again, why haven't you downloaded LFS?
I probably still will at some point down the road. If I bought it now though, I think it'd be a waste of $40. I'd probably play it for a day or two and then go straight back to AC. I can't get enough of AC right now. It's pretty much the only game I load up anymore.
I'm not suggesting you buy it. $20 for the S1 license or $40 for the S2 license isn't great value these days but the demo gives you three cars and Blackwood. That is definitely worth a download and a spin around the track. Blackwood has a rally cross layout which is pretty fun too. The demo is fully functioning and doesn't have a time limit. The only difference between the license levels is cars and tracks.
I've been wanting to try RBR for a while. I really like rally.
I suspect that AC will be my game of choice pretty soon if the new version of the rift is acceptable. Of course that doesn't mean much considering how much I play these days.
edit: here is the link to the LFS download page so you don't have any excuses:
http://www.lfs.net/?page=downloads