Its apparently happened, a guy in a Clio crashed in to a Porsche, went to court and was thrown out because both drivers were aware of the risks involved.
I'm trying to find more information as currently I only have forum hearsay but it sounds reasonable - the risks are clear.
I personally prefer using a car that doesn't need to get you to work. Not only is it less of a worry if you bend it but it also means you can run something with fewer compromises than if it was also a daily.
If you must use a road car that you don't want to damage then my other advice would be don't drive poorly and do things people aren't expecting. Although you'll be slower you still need to drive on the correct lines, brake and accelerate at the correct points and move around smoothly and with sufficient observation. If you can't do that straight away, go out with someone who can first and see how it works. Dithering about off line is more dangerous than being on the pace regardless of the spec of the car.