The the owner of a "hairdresser" car, I'll comment on my own reasons for buying it. I've driven an Elise a number of times and like them....enough to want one if I had the room for a fourth car. But I need a reliable, comfortable car for my every day car and the Lotus just doesn't fit the bill. Also the car has to stay outside so anything with a soft top is ruled out.
I certainly had no intention in trying to find a car that would match the Roadster in terms of "sportiness" , why should I need to? The Z4 is not an out and out sports car, more a roadster but it is sporty enough for my driving and ticks most of my boxes. And heavy and complicated? Aren't most modern cars....excluding your Lotus that is?