Just for reference, the only MODERN American to appreciate in the last 20 years was the Ford GT. And that wasnt by much.
LGT's will never be collector. One could lie to yourself and say it'll be like the '55 Chevy that was a base car in it's day and has now climbed in value, but I feel you would be wrong. The condition a LGT would have to stay in(perfect) and the number of years it would have to stay that way( A LOT) is also only assuming someone will want one after all those years have passed.
A car is only worth what someone will pay for it....