That's because the hottest trend among collectors is classic muscle cars.

"A lot of these cars that we're talking about are really, really great cars, but I think there is a frenzy in the air," said Mark Hyman who operates Hyman Ltd. Classic Cars, a collector car brokerage in St. Louis.

Craig Jackson, president of Barrett-Jackson, a classic car auction company, counters that muscle car values have risen steadily, even right through economic downturns. There are simply more people today who remember the muscle cars they lusted after as kids and now have the cash to satisfy that craving.

Barrett-Jackson's largest annual auction opens today in Scottsdale, Ariz. Several other auction companies also hold auctions at this time in and around Scottsdale. The Barrett-Jackson auction is known, in particular, for high-value classic muscle cars.

"Classic muscle cars" generally means two-door American cars, built in the decade beginning in 1964, with back seats and beefy engines. The Pontiac LeMans Tempest with the GTO high-performance option package is widely considered the first true muscle car.

But muscle car collecting has a twist. Many muscle car collectors don't care all that much about authenticity. Not that they don't want to know exactly what they're buying, but more are happy with a faithful copy or a car with some "improvements" over the original.

While that opens up the market considerably, it also makes predicting future resale values difficult, according to some experts.