Few Testarossas stayed with one owner for 30 years. Those who bought it new got what they wanted. Those who bought them dirt cheap 10-15 years ago got a taste of the dreams of their youth. And those who bought them as an investment at half the price they are now, got what they wanted. I've yet to meet an unhappy Testarossa owner.
I've owned a few borderline supercars but would never go overboard into a proper one. They invoke some violent reactions from people. And lower tier cars as an 'investment' rather than the blue chip stuff are a mirage if you own them for long periods. They'll break even maybe but all that maintenance and taxation adds up rapidly.
It's a different matter if you've bought within the last few years maybe but they're only worth what others'll pay. Not the most liquid thing you can ever own. I think a shit ton of people will be burned with the more modest stuff. Old style BMW M3 Evo Sport's go for up to $150,000. I nearly bought one at $10,000 but it was a dog. That doesn't smell sustainable to me.
Surely if you drive around in them you have to pay huge insurance bills each year. Don't those bills add up to a super car's value after 30 years? An 18 year old would be charged as much as a lambo cost to insure it. A thirty year old would pay much less, but still a considerable sum each year, and that's only if he'd never made a claim.