From Z3 to Z4 (E85/6) BMW kept the same design ethos although totally different in their implementation, and it worked well as an upmarket European MX5. The E89 seems to always have been somewhere in the middle between the pure minimal thrills of the E85/MX5 roadsters and the long established market for high end GT's by the likes of MB and Jag, and as a consequence has never really seemed to have had a market to target and has suffered because of this, the fact that it is a competent 2 seater capable of both a bit of scratching as well as touring seems to have passed the market by.
The moral is once you've the design right, spend your time refining it, not completely changing it. Mazda have recently produced their millionth MX5, their design ethos hasn't altered from the day's of the MK1 when the realised they had got it spot on.
Stu.