You take a chance on any used car, Porsche or not. The 01 you're looking at appears to have been well maintained. (And it's a beautiful car btw...I love the blue top and interior) How often was the oil changed? Do you know? That appears to be at least one area where you can do something to forestall or prevent any major issues.. change the oil at 7500? 5000? something significantly less than the recommendation by Porsche. I change mine at 7500, but whatever you do, change it more often than recommended. Cheap, cheap insurance.
I bought my 01 with 25K on the odo. It now has over 65 K and, other than the driver's seat heater not working, (an issue I think I can fix but just haven't gotten around to) there hasn't been a single problem with it, not one, other than wear items. And, yes, I consider the ignition switch to be a wear item!
Besides it was a $ 25 repair and two hours of my time. I don't baby it... I take it to the track at least twice a year where it gets thoroughly exercised and around town it gets driven, not hard, but not like grandma either.
Regarding the IMS issue. NO one knows the number of IMS issues our babies have had (except maybe for Porsche, and even that's questionable, and they ain't talking). And there's no way to find out. BUT..remember that what you read on the boards is only from the folks who had an issue. And those reports are only from those folks who read these forums... and also only those who tell us about them. There could be/probably are some who didn't report. On the other hand, there are thousands of us who never had an ims problem, or any other major issue for that matter. But since we didn't have a problem, you don't hear about it. These boards, IMHO, tend to overstate problem areas, only because of what I said above. If there were a board around which only catered to what DIDN't go wrong with our cars, well.. first of all no one would read it, but if they did, there would be thousands and thousands of us saying our cars were great, just like me!.
Go for it. Are you taking a chance? sure. Will you regret it? PROBABLY NOT. You'll have a blast with it. But there is a solution to your concern. Buy an aftermarket extended warranty. I THINK (but am not certain) you can get one (from Warranty Direct?) even after the original warranty expires. I bought one, full coverage, everything included, including wear items except brake pads, wipers, tires and a couple of other minor things) when I got my car, solely because of my concern with high repair bills. Fortunately (or unfortunately depending on your perspective) I have not used the warranty even once. Was it a waste of money? nope. not for me. It will cost you somewhere around 2500?? maybe closer to 3000? I haven't checked recently so I really don't know, but mine was around 2200. It was still under factory warranty when I bought it so I'd guess the price would now be higher. Still... that's significantly less expensive than a new engine. AND it covers a ton of other things that might crater on you.
DO IT. You've done your research. You KNOW you want one. You're getting a heck of a deal on the car. Have a great time with your new car.
Bob