The numbers above are well, misleading, I believe. The E89 Z4 is a really low-production car. To put it in perspective, its sales are 1/40th of the 3 series; 1/5th of the 7 series. Its sales are pretty low by any measure. Consider the E36 318ti, which saw about 50% more sales than the Z4 in sheer numbers, but that was when BMW was selling 1/2 as many examples of any model as they do now (in 1998 BMW was selling 50% of the 3 series cars they sell today). Even compared to the modern 6-series, the Z4 has sold 1/3 of those figures.
U.S. sales total for past 7 years - 20,017
2009 - 3523
2010 - 3804
2011 - 3479
2012 - 2751
2013 - 2480
2014 - 2151
2015 - 1829
There just are not many around. (This explains some of the modification calamities we've experienced.) Its design, in my opinion, was superbly executed. Not very well known but the E89 Z4 was the first car designed by a woman at BMW. Juliane Blasi was its designer - she was drawing cars since she was a kid in Germany and wanted to do that for a living. I guess she pulled it off. This video is 2 minutes and worth watching:
https://www.youtube.com/watch?v=fPixOzXUj94 ... they show her working with the contour tape and the clay modeler.
Here's a quote from Blasi, on her Z4 design inspirations: "My desire was to create something like a living sculpture, with sharp lines and smooth surfaces. The main inspiration was an athletic body in which we find exactly this interaction. I can not say whether it was the male or female body ... but I wanted the car to awaken human emotions."
In the last 30 years, I believe the Z1, Z8, E28/E34 M5, and E30 M3 were the only cars produced at this level. Some at a lower level (like the Z1 or Z8). But keep in mind that 20+ years ago BMW sold a fraction of the cars they do today. So comparing production numbers over time needs to be adjusted (just like one would adjust for inflation when speaking of the dollar).
In comparison to other "sporting roadsters", the Z4 has been described as more luxurious in ride -- softer, more understeer, et cetera. The beautiful part about this—knowing BMW M division never worked its version of the E89—is that we can rob the BMW E92 and E46 parts bin to get many of the M3 bits, along with aftermarket springs and swaybars are able to put this car on a more performance-centric plane. Given the highly tunable N54 platform, we are also able to dial up power to near supercar levels. This is a car that, with a comfortable $5k in parts, one can completely transform to a veritable street weapon. A unique street weapon, at that, whose examples are rarely encountered on the road. Expect to see the E89 Z4 less as time goes by.
Filippo