Hey Jeb,
Sorry to hear about your problem, hope it hasn't spoilt the MINI experience.
If the dealer resprays it, it will be overed by the MINI guarantee, they should do a good job too, if they don't make them do it again.
Is the mottling just on the door? If so, how about asking them for a new door? Could then just take the old one off and replace it with a new one - how long would that take???
The dealer is in the wrong here, the car should be fixed to your satisfaction. Don't be afraid to make a nuisance of yourself. You've spent a lot of money on the car it should be perfect (well OK, apart from the rattles

)
Let us know how you get on.