Regarding E85 debut in October 2002, and expected 7-year lifecycle, BMW are to debut new E89 Z4 in Fall 2009. I doubt the car will hit the markets any earlier. Expect M model approx. in early 2011.
E89 will be larger, with folding metal roof, better drivetrain, better tech, better chassis etc. It will be better car in all aspects. It will also look more modern - wearing new generation design elements as seen on CS Concept.
IMO you can surely go for a current E86 Z4 coupe, and trade it sometimes in 2010 for a new E89 Z4.
