What will surely happen is that classic Japanese car values are re-rated over a period of a year or two - once the growing interest in this era (and there certainly seems to be growing wide-based international interest from what I have read) reaches a critical mass of increased demand and comes up against a shortfall in supply. When you think about it, supply is already fairly tight in the 240Z and 1600 lines if you're after investment grade cars, ie original specification in excellent condition with good history.
I note that Toyota 2000GT values are now around $US1,000,000, a significant increase over a couple of years ago.
I'm looking for a good 240Z at the moment in NZ and can tell you that nothing is available, month after month. I have an original spec one previous owner '69 1600SSS that needs company!