Im guessing you havent driven one then, or by "marginally" you mean "the width of the English Channel" - there are less than half as many Caymans as 350's on the roads as well.
Its really good to see that so many people think so much of their 350's, but they just dont measure up to 996's IMO - build quality, performance, image, everything is better in the Porsche, thats why age for age they cost twice as much before you even consider the GT's and Turbots. The Cayman is closer but it was still 30% more expensive when new, at the end of the day its going to be better in most aspects.