My bodyshop suggested the same - he wanted to be sure that they went on nicely, as in removing them they could be distorted and you'd struggle to get a uniform upper edge. New skirts leave less to chance. Took his advice and got a great result as well as a perfect colour match.
He wasn't looking forward to working the textured plastic but, as I reminded him, I was the one paying!
Hardly expensive for a pair of standard skirts, even without TPS discount though, is it.