> some cars even gain value by becoming collectible

I've run some figures. Almost none pay back their storage, maintenance, and tax costs, let alone the opportunity cost of tying up the money.

I remember on an episode of "Antiques Roadshow" where some guy had a couple Leica's his father bought in the 1960s. They were mint, with all manuals, receipts, etc. The amount they were worth was pretty large, and the guy was ecstatic that he'd hit the jackpot.

The trouble was, if his father had put the same money into the S&P500, a completely boring investment, it'd be worth more today than those cameras.

Sure, but I think the point here is that given the option to maximize investment in a depreciating asset (buy fancy car) or minimize that investment (buy an inexpensive car) and invest the difference elsewhere, it's better to do the latter.