Pulling some late night work hours figured I'll pitch in some opinions
my cousin just got an 08 z51 6mt vette and i have spent a lot of time in a good friend's 6mt 370z because i have always loved the 350 and am really close to pulling the trigger on a 6mt 370z, here are some thoughts:
The vette's interior quality is improved in 08 with a new center console. The steering rack was also changed as well as the transmission and the engine. The new LS3 engine makes about 380whp stock with similar torque output and absolutely hauls ***. The z51's 6mt transmission has shorter 2nd to 3rd gears since it's more geared towards track use. The car has a huge trunk so that's a plus. If you keep the RPM around 2000rpm (there is enough torque in the 6.2 motor in a 31xx lbs car to do that) you'll get low to mid 20 mixed MPG; freeway cruising in 6th gear will lands you in the upper 20's and some even break 30's (i can never stay off the go pedal enough to achieve that). not bad for a car this quick.
The only flaws for me are:
the steering feel, and that the car feels pretty big. I like the 370 in that you feel like the car is wrapped around you whereas the Vette feels much bigger than it is sitting inside. Once you get used to the Vette's driving position it'll likely be a non-issue though.
The Vette's center console gets pretty hot after some driving time. Reason being the engine, transmission, and exhaust are pretty much right next to your seat and as far as I've researched there isn't really a way to completely eliminate the heat. Some owners have reported broken cell phones and melted chocolates after leaving them in the center console even in winter time. The removable top also rattles like crazy though that's an easy fix.
Needless to say the LS3 responds very well to mods and you can get it to 500whp N/A relatively easily, and a bolt-on supercharger will land you 550 to 600whp+ and still be relatively reliable. Both cars have good shifter feel - the 08 Vette's tranny is much improved vs the pre-08 Vettes in terms of clutch and shifter feel. That said I still much prefer the 370z's clutch and shifter.
The 370z feels much more nimble and responsive to driver inputs to me. The interior feels tighter and better put together though the Vette in question has about 40k miles vs the 370z with 8000 miles. Obviously the Z is not near the Vette in a straightline but it's absolutely fun in its own way. To me I feel more confident tossing the Z around corners whereas in the Vette I need to sort of trust the car to stay on the road as it sometimes *feels like it could just lose its tail despite its grip/skidpad figures from the mags.
An important point I wanted to make was that to me, the Vette is basically just too fast for the street. It's not that I'm afraid of the power/speed as I've driven several 550whp cars for a good amount of time; in the Vette I basically never go WOT unless I am on the freeway. It just has too much power and the roads in socal don't treat the rear tires too nicely for traction. In the Vette you break the law way too quickly, not to mention all the torque means you don't really need to shift much when you are in the twisties. For these reasons I find the 370 to be more fun and enjoyable on a daily basis as you can have massive fun without necessarily speeding like crazy. It's nice to enjoy a car without needing to do something illegal, it's why I've always found miata's to be mad fun as well, though obviously the 370z is a more complete car IMHO.
If you are chasing power or performance figures the Vette is the winner. If you don't care much for absolute performance figures and just want a fun car to toss around in then the Z is a great choice. If you haven't yet, drive both cars and the choice should be very clear. Good luck
