Z sales, 2002-2014
350z:
2002
13,253
2003
36,728
2004
30,690
2005
27,278
2006
24,635
2007
18,957
2008
10,337
370z:
2009
13,117
2010
10,215
2011
7328
2012
7338
2013
6561
2014
7199
The z33, even it's worst year, sold more units than every year of the z34 apart from the z34's introductory year, in the USA. The Z33, at it's best, sold about 3x more than the Z34 at it's best. Adjust for inflation, the prices are about the same. The recession explains some of it, but not all of it. For reference, Subaru and Scion moved around 26,000 ZN6's in 2013 and 22,000 in 2014. About triple the Z34's sales both years. I think the Z34 is caught in a weird place. People who want a tossable, simple sports car are seeming to go with the ZN6 and people who want something fast are overwhelmingly choosing the Mustang, Camaro, and Challenger. The new Mustang almost makes the Z34 obsolete. Same price for more than 100 additional ponies and just as much, if not more chassis sophistication. The engine of the Mustang blows the 370z's out of the water, it's not even close. Remember when the 350z debuted, it actually had more power than the contemporary Mustang GT. It was essentially a muscle-sports car.
The Z34 has a murky ethos at the moment. It's sort of a benign muscle coupe, it's edginess blunted over time with few, if any, superlatives. The ZN6 and NC are more fun. The Impreza and GTI have become nearly as fast and are far more practical. The Mustang, Camaro, and Challenger are considerably faster. The Z35, in my opinion, needs to be more precise about what it is.
Personally, and in keeping with (some of) the Z's history, I'd like to see the Z35 at around the same power level, but at the weight of the ZN6. A sort of Bruce Lee with wheels. Light and powerful. I think that's a good ethos for the Z. Right now it's sort of an aging middleweight boxer.