Interesting article, no need to compare Z3 and Z4 though as both are completely independent cars.
I like both and would have gladly bought an E85 Z4 which is, in my opinion, the superior car as it's technically more advanced. The reason I bought a Z3 was because it reminded me of my earlier BMWs, although the Z4 further refined BMW's classical roadster design (people should give it a chance and have a closer look at it to accept that).
Plus it's a bit unfair to compare the Z3 to a car that is widely available and didn't yet go through what's (at least here in germany) called the 'valley of tears', means: once the availability declines, prices will start to rise and the E85 will become a sought-after future classic.
Just my humble opinion

Dominik