Over here in Sweden I think musclecars are a good investment. It's hard to say if the prices will keep on going up forever but that's what they've been doing the past 10 years or something.
For example a friend bought a 69 Charger 440 10 years ago and paid about $6000 for it then. It was not in great condition but if he had just stored it in a garage then and not done anything to it, looking at todays prices I'd say he'd get around $25-30000 for it now. I bought my Chevelle knowing that I will most likely at least get my money back if I ever want to sell it. I think you kind of have to look at it as an investment, otherwise it's hard to justify all the expenses.