Good stuff mate. I am also interested in the extended warranty especially as the US boys get up to 5 years - a few more years would be good protection for those of us with totally stock cars, seeing as the Tranny seems to be the most expensive weakest link, even on stockies.
If Nissan still warrantee yours with the Cobb, then its obviously not been launched with VDC off. Nissan are generally ok with mods IMO, but the moment you do anything nasty in it, then gone.
I would recommend you get Nissan's approval in writing too if you can, just in case