Why on earth are you worried about having this repair done and the cost? The other driver was negligent, damaged your wife's car , is insured, and should be expected to make you as whole as you were before the accident.. If you want to drive around in a damaged vehicle, even if only aesthetic, or eat the difference when you either trade or sell the vehicle, that is your business.
This exact thing happened to me in a 1998 Aurora. Rear ended while stopped. That woman wasn't paying attention either. The insurance company for the other driver agreed to pay for to the cover replacement (no damage was found underneath). Apparently the cost to replace was less than a body shop repair of the existing cover because of the labor involved filling in any imperfections before repainting. So I received a replacement. And they matched the paint beautifully.
Accidents happen. But that is what insurance is for. I would like to think that when folks have to pay for their mistakes behind the wheel of a car, they might take that as a wake-up call and pay closer attention the next time. They are driving the equivalent of a 3,500 pound weapon and they weren't watching?!? You are fortunate that your wife was not injured, or anyone else for that matter.
Get it fixed. At the very least your wife deserves a good looking ride.