The best cars going for quite a while, investment wise, were the baby boomer cars - cars that represented their youth, such as the Camaro, Mustang, Monaro, Falcon GTs, XU1s, A9Xs, E38 and E49s, etc. But my 17 y/o son does not think much of these smelly, dirty relics of the past, and I suspect many of his ilk will feel the same in years to come. That is similar to me when I was growing up, where vintage cars were the pricey collectables and the Monaros at the time were driven by teenagers on minimal wages.
As we speak, the vintage cars have since lost many of the high values that they were fetching at their peak of interest (some cannot be given away), whilst the once often laughed-at Monaros are now rarer and more wanted than Mustangs. In other words, cars will be valued to what the market will price them, which is according to the interest they generate.
So my prediction is that the muscle cars that baby boomers are mortgaging themselves to, will have their day of reckoning and fall in value as the interested parties perish with time.
My tip is to ask young guys what cars they most aspire to now, and then focus on these models. The crappy rice burners of the past decade could be a start (if you can get one that's not been violated).