The Z06 and the NSX are both great cars and it appears that the 350Z will be, too. However, these cars are very different from each other. For example, you're looking at one open-top car (the NSX-T) and two coupes. Why? If you don't care about the open top, then consider the '91-94 NSX coupe and save some money.
These cars are very different from each other. What are you looking for?
Acceleration: Z06
Handling: NSX (350Z handling not known yet)
Reliability: NSX or 350Z
Exclusivity (won't see them everywhere): NSX
Purchase Price: 350Z
"Wow" Factor: NSX or 350Z for the first year, NSX after that
You shouldn't have any concerns over the cost of maintaining the NSX. The schedule and cost of routine maintenance is similar to most other cars, as you can see
here and
here. However, you have to be prepared that every once every several years, you may need a repair that's expensive, like a clutch replacement ($2K) or an A/C repair. I think you will find that maintenance on an NSX is no more than on a Corvette or a 350Z once those cars are no longer under warranty.
Have you checked with your insurance agent yet to find out how much insurance will cost if you buy each of these cars? He/she won't have figures on the 350Z yet, but should be able to tell you now how much it would be. Good info to know
before you decide to go ahead with your purchase.