Some good points jr.
I think the 924 is a car that requires time more than anything when repairing it. The boy racer can easily fix his Nova's broken neon glow lights, but would probably find the innards of a 924 daunting (I'm not trying to stereotype here, just I think it's daunting and I'm thinking of getting one!).
The insurance; you might be surprised to hear that third party saves about £100 at most. I found out that insurance companies regard boy racers as a high category anyway, and when they get a 2 litre sports car and go third party insurance, it won't make them much safer drivers, hence the small saving. This is perhaps bizarre logic in one sense, but I can see where they're coming from. I am looking into renting a secure garage in the city, I have heard of some good discounts as a result of garaging a car (something I cannot do at present, as I don't have a garage!). If I could get the insurance below the magic 4 figure £1000, I'd seriously look to get a 924! (My Dad had a 924 when I was a kid, think we even took it to a couple of Porsche Club GB events, although my memory's a bit hazy from all the student drinking meantime).
I think if the person looking for a car is knowledgeable enough in what common issues / faults to spot before buying a car, they won't end up with a dead donkey, and it can be quite reasonable to run. I notice quite a few 924's have 12 month MOT's - not that it is any guarantee, but it's one less cost for the buyer at that point in time.
Not sure if this has been posted before, but a useful resource I found for 924's and 944's on the various models, chassis numbers, common faults, repairs etc. can be found at http://www.connactivity.com/~kgross/FAQ/944faq02.html
For me, though, the insurance is still the killer