I wouldn't buy a Porsche ex-demo/fleet/press car for the following reasons:
It takes more than 10 mins of gentle driving to get the car up to temperature, ok, the coolant temperature may be just up to temperature, but the oil won't be, and the engine block certainly will still have cold spots, and I've seen demo cars caned from off the forecourt, billowing smoke etc. A press car will have been nailed to within an inch of its life, and we all know that its the first few thousand miles that are important as the components bed down with each other, ok, so they make change the discs, pads and tyres, but what about ball joints, piston rings, clutch, gear box etc. They're not going to replace everything!
Ok, you take a risk buying a 2nd hand car too, but I reckon it's less likely to have been driven as hard and for such long periods as demo/test/press/fleet cars. I mean, if you worked in a dealer and could take the Boxster demo home, would you cane it and red line in every possible gear? As long as it's not crashed they won't care.