I wouldn't be so certain that there's going to BE a spyder...
Porsche said with the introduction of the Type 987 Boxster Spyder that it was not
a special edition and not
a one-off. It was a production model that would
be made again. They didn't seem to have any issues selling the 987s either. That's a good thing, since at least in the US the Boxster had one of the worst turn rates of any car sold in the US (average of 250 days).
The hardcore, lightweight Boxster therefore will need its lightweight seats. Until the sport bucket seats exist (which always debut in the GT3) the Spyder will not exist. Therefore the Type 981 Spyder will not be introduced until sometime after the Type 991 GT3 exists. Porsche generally has been pretty aggressive with getting the GT3 out the door (usually 18-20 months after the 911's general availability), so I think 2 years after the base Boxster is a realistic expectation (summer of 2014).
Let's be honest, Boxsters and Caymans don't sell in tremendous numbers. At least in the US, nearly two 911s sell for every Boxster and Cayman combined
. If they are making better margin on the Spyders and Rs, or are getting higher overall transaction prices for them (wouldn't surprise me, since there's some healthy extra margin built into just the S), you can be damn sure they'll make them.