When I got mine I was thinking of going down the getting a cheap run around route and using the Z at the weekends but it's way too much fun to use it just at the weekends! If you're going to buy a decent car there's not point hardly driving it. I use mine as my daily driver and do about 250 miles a week, every time I get in it it still feels an event
You can get sensible mpg out of it, but you have to drive really carefully. I just returned from a 600 mile weekend away and averaged 27mpg and that was with over half of that milage on the motorways, so it does add up.
Also the Z is an extremely comfortable car to drive, I've got no problems sitting for hours on end on the motorway.