Not worth it in the slightest... I know someone with a GTR that uses 100 because he had his car tuned for it... even if you did I would bet the benefits would be very minimal and the price substantial.
Side note, this is why the UpRev maps are awesome... you could have a 100 octane map and a 91/93 octane one... the problem is that requires two different tunes, each with the other type of gas (or just a stock map built in which they all have).