About a year ago here in Frederick the SCCA hosted an auto-X with a very tight course. There was a street prepared 2000 Trans-Am and a 60s model camaro that were in the top 5 overall for there excellent times. These were seasoned drivers who new there cars. They also had a very good handle on suspension tuning and power applications for auto-x racing.
I'm sure these cars wouldn't do near as well in the mud or snow compared to any all wheels drive vehicle. But I wouldn't come close to thinking that one of these car wouldn't have a chance of turning good times at an auto-x. Good Driver + Well Tuned Car = Good Times in any driving competition.