A few weeks back, renown Porsche specialists Autofarm sold a 1973 Porsche 911 Carrera 2.7RS for £500,000. Once I’d read the release I felt the need to read it again to see what I’d missed. Was it a very rare lightweight model? It was not. Had it been built with right hand drive? Again, no. Had Steve McQueen once broken wind within a half-mile radius of its duck tail spoiler? Not even this.

It is by all accounts a lovely car in wonderful condition, but nevertheless a standard, second series left hook Touring model. And it went for half a million pounds. I can remember gasping at a very similar car advertised for £225,000 only two years ago. It would seem to have more than doubled in price since.

Indeed it appears that £225,000 wouldn’t today even buy a good 993-generation RS, a fact I find especially painful having sold mine a dozen years ago for around £190,000 less than that. I am told that the most desirable 2.7RS – a right hand drive lightweight – is now comfortably over a million pounds.

I bow to no-one in my fondness of these cars but I do find myself wondering if prices have been far too low for far too long, or whether in fact the anomaly is right here and now.

Nor is this a curiously Porsche-centric phenomenon. I recently met a chap who ignoring all the advice of his friends bought a total wreck of a Ferrari 246GT for £40,000 two years ago, spent £110,000 restoring it to concours condition. He has doubled his money in the process.

F40s are now regularly advertised for £750,000. It seems only a blink of an eye ago they were £250,000. At its forthcoming Pebble Beach sale, Gooding’s has an F40 currently guiding at $1.2-1.4 million. And you can find similar tales to tell with Astons, Jaguars and almost every kind of classic car.

The question is if it will last and if so, for how long? I am entirely useless at looking into the future, because if I’d had any talent for it, not only would I never had sold the bloody RS, I’d also have bought the mint 246 that could have been mine for £18,000 back in the 1980s.

But I do remember the end of that decade and how prices spiked back then. I have in my hands a copy of Autocar & Motor, dated August 2, 1989 and in the back there’s an ad for a delivery mileage Ferrari 328GTS priced at £119,950 despite a list price of under £50,000. Just over a year later Graypaul advertised another 328GTS with 195 miles on the clock for £66,950 – still over list but a terrifying fall in such a small space of time.

Are we heading for another such collapse? I doubt it. The market is a very different place now and the big winners and subsequent losers then were new, low volume sports cars with long waiting lists and a customer base with a strong affiliation to the Gordon Gecko school of business studies.

What I find notable about what’s happening now is that only the most rare and extraordinary new cars appreciate at all, and while most alleged classics are increasing in value, the meteoric risers are genuinely special machines.

Even so, it cannot continue to spiral upwards forever. Can it? The great unknown is what will happen if China ever opens its doors and its eyes to classic car ownership. There is no classic car culture there at all: car manufacturers displaying heritage models at Chinese motor shows are often asked if by punters if they can order a car that might be half a century old.

I’m told by some that taxes on exporting such cars to China would be so crippling as to void any chance of a profit; others say it’s simply not possible at all. Then again China remains the fastest changing country on earth, so who knows how long this particular status quo will last?

In the meantime I think the old rules of classic car ownership apply more than ever. Buy a car that was good when it was new and one with as strong and verifiable history as possible. If it is rare so much the better, and if it is good to drive, technically interesting and historically important these factors will all contribute not only to its value but, more importantly, its ability to retain it long term.

Above all, buy the best example you can, even if it means paying over the odds for it. One thing that has not changed down the years is that the most expensive cars often turn out to be the cheapest, and vice versa.