There's a hell of a lot of speculation going on in the "classic" car market at the moment. This frequently happens when other forms of investment aren't giving a return. I spotted someone trying to sell a rusty 1.0L Vauxhall Nova 3dr with 220,000 on the clock for £4,000 as a "classic" last week. This week there's someone advertising a tidy, middling spec 944 Lux with 75k on the clock on Autotrader for £25,000 (no, I haven't mis-typed that).
944s are benefiting, to some extent, from this speculative surge in prices. The bubble will burst in much the same way as it did in the early 90s. It will burst when conventional investment opportunities start to improve and speculators decide to "cash-in" on their classic car "investment" en-mass, putting their money back into something they understand (and that doesn't rust and require maintenance). Classic car values will drop like a stone back to their pre-bubble values as supply exceeds demand.
The real rarities will be somewhat price-crash proof. 944s won't be, there are still too many of them around. The trick will be to judge the top of the market and sell just before the crash
Much as I'd like to believe the 944 is now being appreciated for its fine qualities as a sports car, I don't.