The Touring does seem a very attractive price, but it does have the "worst" (or should I say, least powerful) engine of the range, just a single carb 2.5.
The SSZ on the other hand has the "best" (i.e. most powerful) engine 2.8 triple carb, it is also a Zagato body which does help, even if it is perhaps a little overpriced. So I would say yes it is purely rarity/exclusivity.