[Dave S.]

I haven't upgraded the IMSB in my 2003 S (24k miles). Seems spending $3K + on an insurance policy that you don't know if you need seems pretty steep on a $20,000 car.
If it fails, I'll either sell the dead carcass for a few thousand and never buy another Porsche again, or maybe take advantage of the situation and try to find someone with experience installing a 3.8L 997S engine into it and make it a rocket.
If I ever have the transmission out and am replacing the clutch, I would probably do the IMSB for good measure, just not willing to spend that much for nothing in hope that I'm fixing a problem.