Acura NsX Pilot hit the nail on the head. Coming from a heavy economics/finance background, I think a little differently than most regarding a car's true value.
Overall cost must factor in insurance, fuel mileage, maint., and depreciation. Tires and just about everything else is going to be more expensive on the NSX. But if you are smart buyer, you will probably end up spending less money within a 3 or 5 year ownership with the NSX. The only reason this may not work effectively is if you plan on putting a large amount of miles on the NSX.
Since I can't stand losing money on any asset, including cars which can be extremely difficult, and have decent mechanical experience, I'd go for the NSX. If you don't want to deal with owning a 15 year old car [I also have a 91 LS400], get the 350z. The overall performance of the two is remarkably similar, but one drive in the NSX and the 350z will never feel adaquate.