Yes good that they took the initiative rather than you having the problem sometime in the future. Though I can't help think that I'd be more than a tad miffed at having a 5 yr old car that had to be totally resprayed. No problem if it's a keeper but if I were looking for a second hand one I'd avoid one that had a total paint job.
The MB dealer said that as this is a Warranty job it wouldn't be disclosed when selling the car as a used car, unless a customer asked to review the full service history.
So it will have NO impact on the residual value or on the part exchange value it we change it.