The club I shoot at is USPSA (IPSC), while I'm much more IDPA-oriented.
I wouldn't label IDPA as like NASCAR since NASCAR isn't a good comparison, and not real practical.
The biggest problem I have with USPSA (IPSC) is the Production and Open Divisions. The Production Division is an old artifact of the "old" AWB Days with the 10 rd magazine capacity limit, whereas if you want to use a "modern" normal-capacity handgun (>10 rds capacity) you have to shoot in the Open Class with the "tricked-out" expensive guns. Not real practical IMO. USPSA needs to fix that.
While my USPSA (IPSC) club is what it is, I'm not into the "game". While I'm always stuck in the Open Division with my XDm 5.25 and every-day carry gear I'm at a disadvantage compared to the "high-end" shooters, but I don't care since I'm just trying to become a better shooter and have fun.
Alos, I wouldn't call USPSA and IDPA seperate sports since they're are one sport but with different philosophies.