I wouldn't trade my M3 for it (not even close), but I'd love a Z4 as a 3rd car, just to drive during the spring or take it to Charleston. It has to be one of the most beautiful cars BMW makes right now, along with the 4er Concept and the M6 in my opinion.
Current: E92 M3 Sparkling Graphite/Bamboo Beige/6MT. E36 M3 Techno Violet/Dove/5MT. E85 Z4MR Alpine White/Imola Red/6MT