I'm not sure the Z4 and 370Z are aimed at the same market. I've become a great believer in "fit for purpose" over the last couple of years and there's no doubt in my mind that if I wanted a focussed sports car, for country lane strops and perhaps the occasional trackday, of the two its got to be the Nissan. On the other hand, if they are not your priorities and you just want something a little flash, comfortable, quality feel, nice interior and a relaxing drive after a hard day, then the Bee Emm may be a better bet.
On the highly subjective matter of looks, I'd take the Z4 over the 370 any day of the week.