Performance wise, GTR is a threat to Porsche, on Paper. However, few Porsche drivers will buy that car. That is why GTR demand has dropped to MSRP level just couple of months after introduction. GTR's biggest fans are JDM lovers, they come from Civic, EVO, STI, S2k, 240SX, and they can't afford that car.
Nissan shot them self in the foot for doing this - A car that is very well priced but still over priced for average ricer, and with Ferrari Maintenance cost. Even if a guy squeeze every penny out of his ass to buy the GTR, You will them dumping their barely used GTRs to avoid any potential out of warrantee repair bills. When that happens, new GTR price will come down down. By this time next year, you will be able to buy a brand new GTR at invoice and probably with 0.9% interest; in fact, Nissan dealers will be so desperate in moving this car off the lot because they don't want to sit on $70 grand credit.
What ever the marketing strategy they called "GTR Certified dealers" will loose their slogan because all of the none GTR certified dealerships will start to get GTR in stock, just so Nissan can move the cars out of the production line. This car will hit the same fate as the NSX, except couple of years faster.