I understand there is a lot of economic forecasts at the moment claiming it's the end of times. Covid-19 has obviously brought to light a lot of problems in Global Markets. The housing markets and the volume of debt in them does seem to be a problem. But I think the biggest difference between the vintage car market and housing market is that in order to buy a house most people need a mortgage (a sizeable 1) and so when they lose their jobs they can be forced to sell at the market value (in a real estate market crash there is a limited pool of buyers).
However with vintage cars, a bank is unlikely to give you a loan to purchase a vintage car, unlike a modern car from a dealer where they are willing to extend finance. This is because it's easy for the bank to see the market value of a new vehicle and the loan against it Where as for vintage cars (especially a project car like the rusty car in Sydney) no bank wants to lend on something like that, since their analysts have no idea as to it's market value.
So in order to purchase such vehicles you need pocket money, and therefore you're not on the hook to a bank etc.. should the market turn down. I think that's 1 key difference between vintage cars and the housing market.
Now will some be forced to sell assets if they have over extended themselves? Investment property loan gone sour or the like? Sure they might liquidate the classic car etc.. and you may find a cheap deal.
But we have just had the largest economic downturn in 100 years and the demand for a rusty bucket like that 73 240z on eBay is still through the roof! Which surprises me, but then again if you look at the wider Japanese classic car market everything has skyrocketed. And Covid-19 lockdowns means that people are looking for a hobby to do at home. So that's driving demand for project cars.
FWIW I recall when Mazda R100's were selling for $20k+ in similar condition not long ago, there was a lot of gnashing of teeth and complaining. But R100s have been selling for 6 figures for years now and prices haven't crashed. I think 240z/260z's have finally been recognised after spending many years undervalued, which at least means more support from the aftermarket for parts etc..
It should be noted that sometimes classic car values drop and it's often driven by demographic shifts. 50's cars have been in decline for a few years now, because the demographic (Silent Generation) who was into them have been dying off. The thing with S30Z's though is that they were always a Boomer favorite, but Gen X grew up buying them for cheap in the 80s/90s on the second hand market. I was an early Gen Y (tail end of Gen X) and bought 1 cheap in the late 90s and the newer Generations seem to love the S30z as much as all the generations prior. That's the thing with these cars they tend to transcend generations due to popular cultural references, video games, car restoration programs, the thriving culture of 90s performance Japanese cars (which has drawn people to look to the past), the hype around Fast and the Furious franchise (with a focus on GTRs etc..) but you'll note the older C10 GTR values are starting at $200-$300k+ along with the PS30 (Z432)'s in a similar price bracket (and 432-Rs in the $1M range if they ever sell or come to market).
There just is not many cars left anymore, and by putting together the HS30 registry and data, along with the photo albums of what's around still. I'm hoping others can get a clearer picture of why the market is being driven up.