My number plates were £20 each, why should I be £20 out of pocket because of someones negligence, and have to put up with them breaking the law by driving away from an accident they've caused? And sometimes, adding a non-fault claim to your policy will result in no increase in premium anyways.
1) You were ripped off
2) For the cost of a tenner, is it worth the risk?
3) What if you have a second non fault within the next 5 years? One may not put it up but two almost certainly will.
By all means report it to the police as a hit&run but it's best to keep it off the insurance databases.