If there was no significant damage to my vehicle, I'd probably let it slide as long as the person was nice. If they were a dick, I'd probably press for new paint over a scratch. Poor or rich wouldn't make any difference to me, although if they couldn't afford it I'd be open to bartering or trading for services.
As to the moral obligation to fix, that's a novel idea. They've decreased the value of your property, so the money you are compensated is not a gain. It would be no more immoral to save it or use it for something else than to fix the damage, as it is after all your car and your money.