I am in a similar position. I currently use my M3 as my daily driver and my wife recently had a baby. I thought about replacing the M3 with a cayenne GTS or turbo. We needed to buy a 3rd car for our nanny to use, so we ended up buying an E350 wagon. Now that we have that as a 3rd car I've decided to replace the M3 with a 991 S coupe instead. It will make a great dd, is a blast to drive and the wagon is available when I need to carry more than the 991 can accommodate.
My advice would be to not worry too much about putting miles on a car. I have little interest in buying a car that will spend most of its days sitting in a garage. I drive my cars and enjoy them as much as I can. These cars are way too expensive to just drive occasionally on the weekend. Just about every modern car is going to depreciate quite a bit no matter what, so you might as well enjoy them as much as possible.