[Perfectlap]

Warranty Direct will charge you at least $1000 per year for bumper to bumper coverage. I would be inclined to continue doing business with your dealer.
If your actual mileage is over 40,000 then I would definitely consider it to be worth while. The 2003-2004 Boxsters have had some complaints of intermediate drive shaft failure, that could be a very costly repair if it rears its ugly head.
Find out who exactly is writing the coverage for the dealer extended warranty and google them.
Tell them you are deciding between warranty direct and see if they can lower the price AND extend your payments (interest free of course) over a year or something.

And get a full top to bottom inspection before your coverage runs out. Takes about a day in the shop. Well worth it.