Cars like the 370z are nearly extinct in today's car market. There's practically no sports cars in its price range that actually compete with it. The closest competitors to it are the Boxster ($48k+ MSRP), Cayman ($51k+), BMW Z4 ($48k+). The Z starts about $10k less (of course you can option it much higher) and can offer similar (or better) performance to these other cars.
The closest things on the cheaper end of the scale consist of the Subaru BRZ/Scion FS-R, Miata, etc. The STi and EvoX could potentially belong here for sake of those car's performance, but they do not fit the "sports car" bill, sorry Suby and Mitsu fans!
The problem is those little cars simply cannot keep up performance wise when you compare them to the 370z. The Z is in sort of this middle ground where it's powered by a (relatively) large displacement NA 6 cylinder. It doesn't have any sort of F.I., meaning that it has less tuning potential at the same price point (i.e. $3k into a FI car gets you much further than $3k into an NA car). So it's not sporting a smaller size 6 cylinder with FI nor is it powered by an NA v8 (like the Mustang GT or Camaro SS, which are similar in price).
So what you end up with is this sort of unique car that doesn't seem to fit into any other categories, isn't seen often on the road, and offers true sports car feeling and performance all in "fairly" entry level price point. I kind of enjoy this notion of minor exclusivity at a fairly cheap price. I hope I'm not taking this too far, but you're almost "pigeonholed" into the 370z if you're looking for a sports car that makes around 350hp.
So now I'm coming to the real meat of my post; I apologize for the massive introduction. There is no real DIRECT competition for the 370z, that's why you see it getting roped into comparisons with the Mustang GT, Camaro SS, and Challenger SRT8 (i.e. the muscle car crowd). The Z's legacy lies in 6 cylinder engines, but times have changed. Honestly, I enjoy seeing the return of muscle, I'm a huge muscle car fan and I love the idea of bang for your buck, that's the heritage of muscle cars.
My idea is that Nissan should use that "miniature Z" platform to produce a new model that hails back to the 240sx. Make it into a small "sporty" car with a turbo 4 cylinder, back seats, and rivals the performance of the Scion FR-S/Subaru BRZ (give it a bit more power, it's great to create more competition). Meanwhile, take the 370z into the v8 direction. Develop a version of one of their existing v8's, call it a VK56VHR (I'm not too good with naming schemes) and make it a higher-revving performance oriented version of the existing 5.6L.
So now they offer a turbo 4 cylinder sporty car that could hint at the later year 240sx (97-98, or "kouki") styling. The G37 is still available if you want a sporty 3.7L NA v6. Even the sedan's that Nissan offers can still be "peppy" with the 3.5L v6.
Lastly, the Z is now a v8 powered sports car that doesn't take the back seat to the muscle cars, while still managing to produce that euphoric feeling of driving a sports car!
Of course all of this is just pure speculation and sort of a pipe dream of mine...
