transmission failures are probably over reported. having said that, the full price for 'repair' is misleading as nissan only appear to do swap outs.
perhaps Martin can chime in here with his experience in the cost of transmission failure repairs.
the cost of tracking the car (if you are into that) with nissan over a couple of years before the warranty expires probably negates the benefit of the potential cost savings of the warranty to some extent. some of this may depend on how you negotiate servicing with the dealer, track frequency and other factors.
be aware though, once bitten by the performance/track bug, you will be spending more money on consumables and performance parts than on a tranny as many on this forum can attest to!