should i buy the aftermarket warranty?

Richard, on a new Boxster, an extended warranty is more like $4,000. If you put that money aside, when the Porsche factory warranty ends, you'll have about $4,700 (assuming a 4% yield) for maintance repaires.

Like I prefaced in my post, I am not sure if this holds true for the more expensive than average P-car maintance.

You are right about the sample size. For example, if everyone on this forum sent you $2K for an extended warranty, that would be about $7,000,000. That would cover a lot of potential claims, including 3.5 blown engines (using your example of 1:1,000).