The XGA is an april fool's joke.
http://www.s2ki.com/Home/index.php?o...d=252&Itemid=6
That said, nobody knows what will become of the S. The NSX has supposedly been 'on its last legs" for the last 4 years of production, and yet, Honda keeps trying to sell 'em.
As far as collector's item premium. There are plenty of cars around in the used market. It will be some time before you'd need to worry about a premium to get a hold of one. I've seen some MY 2000 ones advertised for ~12K albeit with lots of miles on the odo.