Interesting perspective, thanks for sharing.  Some counter perspectives:

I took the GTR to the track several weeks ago and it was like close to 100degF.  I had 4 20 minute sessions on Infineon raceway and only once did the gear box temp exceed 230degF (110degC), and that was for like a minute or so.  Brakes felt the same throughout the session.  Maybe I wasn't pushing the car hard enough like your friend?

Nissan does recommend changing the gearbox temperature once it exceeds 110degC within like 5000km or so.  But I think there needs to be a certain duration at the higher temps in order to require a gear box oil change, based on Nissan's computer diagnostics.  Several people I know of have been to the track like 2 or 3 times with the GTR and the computer analysis shows that no gear box change is required.  Oil analysis confirms this as well. 

However, the front differential fluid is recommended to be changed more often, but that is relatively cheap to do.

In the US, the warranty is not affected by going to track.  I guess it's different in Europe?  Does this apply for non-compettive events as well?

Yes, warranty is voided if VDC (ESP) is turned off.  But thus far, many people have not found many reasons to do so yet.

Thus far, I have averaged about 19mpg in mixed driving, over several thousand miles.  So mpg is not that bad.