"The rarest classic cars are selling extremely well and the prices are going in one direction. Ferraris have become the equivalent of Google stock."
This West Coast series follows a Bonhams event at Goodwood on July 12 that raised £36.1 million ($69.5 million), a record high for a classic-car auction in Europe.
The £19.6 million paid for a 1954 Mercedes-Benz W196 that Juan Manuel Fangio drove to two Grand Prix victories was a record for any car at a public sale.
"The NART Spyder is the car everyone wants," said Kidston. "It's only had one owner and never been on the market. They're so rare. I wouldn't be surprised if it made US$20 million with auction fees."
The 275 NART Spyder - named after the North American Racing Team - was the brainchild of Ferrari's North American importer, Luigi Chinetti.
"One of those red Italian things," is how Dunaway described an identical car in a scene in The Thomas Crown Affair.
Dunaway's co-star, Steve McQueen, bought one of the 10 models, as did North Carolina businessman Eddie Smith, whose family are the sellers at RM. The convertible would have cost about US$15,000 at the time.
Of the 120 cars being offered at RM's auction this weekend, 25 are expected to sell for more than US$1 million.
A 1953 Ferrari 375 MM Spyder commissioned by Jim Kimberly, heir to the Kimberly-Clark business empire, is valued at more than US$9 million.
Classic Ferrari racers from the 1950s and 1960s are the world's most consistently valuable motor cars.
A 1957 Ferrari 250 GT 14-Louvre Berlinetta is the highest-priced lot at Gooding's 10th anniversary auction at Pebble Beach this weekend.
It is one of only eight surviving examples, with a race history that includes a fourth in its class at the 1957 Mille Miglia, and its price is estimated at US$9 million to US$11 million.
Bonhams sale will include a 1931 Le Mans-specification 4.5-litre Supercharged Bentley "Blower". Owned by American collector Charles RJ Noble for more than 50 years, it is predicted to fetch up to US$5 million.
Although pre-war cars tend to be less fashionable investments than postwar Ferraris, another example of a Bentley "Blower", dating from 1929, sold for £5 million at a Bonhams "Goodwood Festival of Speed" auction in Sussex in June last year.
The racer could go as fast as 220km/h.
Last year's sales by Gooding & Co, RM Auctions and Bonhams in California raised more than US$220 million, a 33 per cent increase on 2011.