always buy a car for the purpose.
a z4m is a sports car (pure and simple) . People who buy it normally value mileage, condition, servicing history, crash history, mechanical soundness as the most important parts. That is because you are buying it to enjoy the "sports" nature of the car.. By all means, if 2 identical cars are presented where 1 has all the options and 1 doesn't, it will be a no brainer as which one to pick.
But, no 2 cars are identical mechanically. As such, because you are not buying a high mielage family transport, it is more important to buy on mechanical condition than on options.
Before you ask. I bought a car that did not have sat nav nor HK DSP sound system. It had 11,000 miles (at time of purchase), full service history, tracking straight, interior looked barely used, never seen paint other than at the factory and engine felt super strong. That's why I bought the car. The fact that another leggy example had sat nav, rear parking sensors and pro DSP did not dissuade me from why I should be buying based on conditions and not options.