Let's say I brought my car back to a 'showroom' new finish (removing dents, chips, scratches, swirl marks, etc.). How much value do you think I'd gain? Would I make money on the investment to detail the car?
I would agree with KC. As a buyer you know what you are going to max out at and pay, but if you walk upon a real cherry you might spring a few extra bucks for it over one that looks like every other car you have been checking out for the past 3 weeks. It will definately help you to sell it faster even if you don't get much more money.
But on the flip side you could get some sucka who hasn't done his or her research with very little time and too much money that might just dearly overpay for the thing because it looks tight.
My view is that for the fairly modest investment for a good detailing job, it is well worth it prior to selling a car. I think most people will place high value on their first impression - what the car looks like! It also sends the message that the car is "taken care of" - assuming that mechanically everything is in order.
I have always detailed cars before selling them - almost always, the first person who looked - bought the car.