Would be cool but only if the AI were revamped to be more aware of you on the track, as is the AI will move over and take you out far to often and if damage were enabled would cost you lots of credits and make the game much less enjoyable.
With better AI it could be a good addition but AI must come first
Also note that it should not be "pay with your gain" It should be damage persists until repaired and the repairs should cost a realistic amount quite possibly much higher than the prize in the race you are in, depending on the car of course.
Crashing an FXX in a race that only pays 40K would set you back a very long way. possibly 400k or more in repair costs
