A guy we used to race with on rF2 for a while there (Voltaic) has it. He enjoys it. Not sure it's my cup of tea though.
Speaking of Game Stock Car, I think I read that the 2013 update is coming soon.
I often wish I could find more GSC players. Having about 25 guys in a race series, being able to accurately replicate a real life series is one of my biggest "sim dreams".
It's not something that I'd buy but it would be neat to have in GT. Although then people would complain about why they didn't choose another supercar instead. It reminds me of the made up race series that they sometimes have on Top Gear like the People Carrier touring series (minivan). As an aside, Max Chilton usually appeared in those which is why I kind of hope that he does well.
As for replicating a real life series, I've decided that the closest that I'm going to get to that is iRacing. I'll probably never find a league that will run at times that I can do. iRacing kind of replicates some real life racing series but instead of having to race at a very specific time, you can pick the time that you want to race. At the higher levels, you get pit stops, full course yellows and everything. iRacing is kind of like Apple. It's expensive, it isn't perfect, but the overall experience is very good and not matched by any other game.