Let's face it. People buy cars like this for their fun factor, and perhaps for their "cool" factor as well. The Z4 does a bang-up job of providing both while delivering upwards of 25 mpg. It's a bit of a chore getting in and out, especially for a 6'2" guy like me, but once you're inside it's surprisingly roomy if you lower the seats all the way. The power convertible top works perfectly, and the interior is gorgeous. The ride is stiff, but the car runs and handles fantastically. My only complaint: you have to be careful when parking or you'll scrape the underside of the front cowling.
Fun to drive, convertible top, exotic/cool styling that gets lots of "oohs" and "aahs."
Add a couple of inches to the length and make the cockpit just a smidge larger. Raise the whole car another inch or so off the ground. Add some kind of guardrail or bumpers to protect the front end or have a built-in curb sensor. Do something about the cup holders. They're terrible!