I too have been wondering why the prices have gone up so much.
18 years ago, I sold my 3 owner Australian delivered '76 911s with 222km for $18k - boy do I wish I had that in my shed now. Well, actually if I had it, I would sell it. I liked it, but I personally think they are a bit too old to be practical. I didn't like the lack of air, the pre-unleaded smell, the bump crash handling. And it wasn't all that reliable either. But, I do (did) miss the whole 911 experience - it's like nothing else on the road.
About 7 or 8 years ago a friend of mine was looking to buy a one owner 964 C4 in white with 9km for about $55k. I was saying to him, that I felt my BMW 335i was a better car for about the same money. It was quicker, had more room, more practical, felt (was) a lot newer. Now, who was right? - he has well and truely doubled his money. During the same time, my once new 335, has lost $100k.
A few months ago I started getting the itch for a 911, but just couldn't justify the high price, so I posted on Bimmerpost forum on 911 values
I just couldn't see why an 11 year old 997 could be worth the same as a 2 year old BMW M3. But the reality is it's all about supply and demand - they aren't making 996's anymore - light weight, flat six sound and feel, yet reasonably new and comfortable enough to easily drive everyday.
Anyway, I must have FOMO, so I just had to join the 911 club, here's a photo: https://imgur.com/a/Cka9n5X