I also think we're in a bubble. Two years ago, a friend in FL who had a RAIV GTO told me his car would be worth 40 grand shortly. I told him he was insane - after all, cars went up in price 15 years ago after the stock market crash, then settled to a point of sanity. However, he has proven me wrong . . . and then some.
Analyzing the situation some more, I've arrived at this conclusion (and, of course, it may not hold water as my previous opinion on prices was wrong too!)
Baby Boomers are reaching 60 next year. They are at a point where they are retired or close to retirement. They have a lot of disposable income - a lot more than when they were younger. Maybe now they can afford the car they couldn't in the 1960s due to funds or family. Maybe they want to find the car similar to that they owned 30 years ago. So many of them are doing so.
The stock market has been down for a few years, so people are looking to put their money in other things. This is just like the late 1980s. Once the stock market goes up, I think prices will soften a bit. However, I don't think they'll sink to prices that are sane. That's cuz people still want to relive their youth and they can afford to do so. There are more musclecars now than there were 15 years ago as people have been saving and restoring them. But, despite the slight increase in supply, the demand is higher too. This will keep prices high.
This is why I made my comment earlier. Once the Boomers die, prices will go down to a point of sanity. Demand won't be there because Gen Xers are not into these cars as much, and Gen Yer even less. But it seems to be the case that people don't mind paying insane prices for these cars because they want to enjoy them in the twilight of their lives. Life is not forever, after all.
The only amusing gripe I have for all of this is the relativity of it all. Is a Hemicuda hardtop worth the same amount as a Mercedes Gullwing? I think their values should be related, and you don't need to tell me which is a neater car. Alas, in the end, it all comes down to supply and demand. Take the Mopar and the Merc to Germany and see how their values differ.