I never found autocross to scuff my car except hitting cones. Clear bra on the front bumper works wonders for protecting the car on the street and track.
The track does tend to get the front end chipped up, particularly if you run the advanced group with lots of slicks etc. around you. Keeping back from other cars when you can decreases that risk. I've seen people apply painters tape to the whole front end, but I've never done that myself.
I track my cars a lot, and the only way you can tell is the rock/debris chips on the very bottom of the front bumper. Not a huge deal.