In the business section of the New York Times yesterday: article about an economics professor from University of Chicago. He's advanced a theory that seems to have some merit. He traced some of the heavy hitters from Sotheby's, etc, trying to figure out why some Cezanne's were worth a million, some worth multi-millions.
The difference, according to him, is the time when these works were made. Some artists (he referenced Picasso) peak early in their career. Some, like Cezanne, work studiously until later in life.
Don't have the article title--sorry--but thought it might interest you guys.