For example if I could afford a Shelby Cobra GT500 and own and drive it moderately would it be wothwhie to get it and sell it in 30 years ? case in point a Yenko 67 Camaro is worth over 400k now!

i would say it is your call and as for value the vehicle is only "worth" what someone is willing to pay, as is with all other items for sale. just look around and you will see what people are willing to pay for items, case in point a used pentium 2 based laptop has an actual value of 200.00 to 275.00 people are willing to pay no more that 150.00 for one as seen on the net. you may build a desktop pc tower and have 1500.00 to 2000.00 in the tower alone and you will most likely only get a max of 300.00 when you go to sell it. i think if you are looking to buy anything buy it because you want it and not because you plan to sell it later because if you buy it to sell it later you will most likely get burned. i (if i had the cash) would pay up to 1200.00 for a 1949/50 chevy 5 window pickup but for 1200.00 it would have to be completely restored to factory original, and this pickup happens to be my "dream" vehicle. there are poeple who will pay more and some pay less but it is just finding someone willing to pay you what you are asking.

go to the barret jackson web site thats the auction on speed channel that maybe able to help. if you could get your hands on the new gt350h that they just released earlier this year you would have something. there was a low production of them. vin code 1 sold for over 100k the rest went to hertz for the rental and when they are done they will be sold or auctioned later. they closely resemble the original

Nobody can really answer that, there's no way of knowing what cars will be worth. Keep in mind, those million dollar Mopars and Shelbys etc., were cars that all red blooded boys in the 60s wanted to drive. Those same people are the ones driving up the prices now, but 30 years from now, most will be gone. Will the current generation still hang on to cars like the boomers have? Will a $50,000.00 Ford really spark the same love affair that muscle cars of old managed? Is anything that is built to be collectible, really all that collectible? I kinda doubt it, but who knows?
Finally, will there be any gas around to power a collectible car? If not, will anyone really pay big money for a car that they can never drive?
Buying a car just doesn't sound like a good retirement plan to me.

Drive it moderately for 30 yrs. and you'll probably stand a good chance of wreckin' it.

Might be worth something as a parts car though :}