My yearly mileage is very low, so fuel consumption is not a practical concern.
For me, everyday usage raises other issues:
On the MINUS side ... and these comments apply to almost any sports car ... there is a fair bit of stress involved in just doing basic everyday simple things:
a) The front bumper is low, so one tends to graze it in parking lots that have those concrete stoppers (they are meant to stop the wheels going further forward .. but they get your bumper first).
b) Parallel street parking: with the 18 inch wheels, the rear wheels sit out further than the front ones, and one tends to graze the alloys ... no matter how careful you are. Terrible sound ... specially when you have just had them fixed up

. You pop out for five minutes to get some hot bread, and scrape the wheels ... not good economics.
c) The doors are big ... like any coupe ... so you have to be careful in parking lots. Actually - just avoid internal parking lots
d) Because the car is small and low (like almost any sports car), you sometimes worry whether people have seen you on the road. I try to keep clear of buses and trucks.
e) The ride on OEM run-flats is hard
On the PLUS side:
Most of the above comes with the territory ... if you want a sports car. But in the Z4's favour, especially:
a) the Z4 coupe really has quite a practical boot ... especially when the roller-blind is open ... you can fit large boxes in there, as well as big suitcases if giving someone a lift to the airport!
b) It actually works ... usually brilliantly ... unlike other exotic sport cars.
c) Pretty low maintenance ... other than feeling compelled to clean, and remove the brake dust
d) Superb interior ergonomics
e) It's enormously fun to drive anywhere. And gorgeous to look at everywhere
