Great ideas, thanks, I will use them.It will depend on what type of car you want to represent.
Most race winners are in pretty good shape at the end of a race - look for cars (videos and images) before the track celebrations/burn outs, on the way to and in the winner circle. Another representation I've seen is to show them covered in confetti and beverages.
Different races will also have a different level of race wear. Bristol, Darlington, etc will often have flattened sides, caved in noses, corners, etc.
Basic steps is to add tire dust and debrie - sand down real rubber and sprinkle it on. Sand paper over paint/decals/stickers to show wall rubs. Paint on wheel circles from side by side racing. Hot water baths and various implements will cave in or misshapen sides. Add electrical tape (bare bound) to simulate pit road repairs. Cut away fenders, rear end, noses to represent wrecked cars.
Sand paper wheels to show wear and dull coat for age.
You can also spray on dull coat vey lightly from the front of the car to simulate dust wear and oil build up over the nose, hood and windshield.
Be sure and take photos to show us how your track wear turns out! 🤙