most importantly, they will be when she is turning in the over-mileage benz (or has to purchase it because of the over-mileage).

Thus, it is not an emotional decision but a financial one. And something tells me that the correct financial decision is to avoid putting additional miles on her car at all costs. You may love the low mileage on your '02, but other than losing your warranty quicker, miles on your car are not nearly as valuable on an '02 A6 as they are on an '08 Benz that is under lease!