I have a vehicle that has a similar commute, it also has errands etc, but rarely runs for more than 30 minuets at a time, all in town. No special warm up, just start and go. I change the oil twice a year with cheap synthetic and orange frams @ a cost of $20, I never even look at the odometer.
Don't bother harping on your wife to walk or ride a bike. It's a nice luxury these days to work so close to home. The time saved covers the cost of an extra oil change.