What do Old Master prints, 19th century American paintings, vintage photographs and the works of Jean Dubuffet have in common? All represent above-average investment potential says Blodgett, who notes too that the hottest paintings today (and heading for devaluation?) are 20th century masters, the bluest of the post-1945 blue chips--Pollock, Lichtenstein and Johns. Don't get serious about collecting unless you have $1,000 to invest; $5,000 to $10,000 is better. And don't spread it around: Blodgett's two keys to a sound portfolio are quality (buy the best piece you can afford and try for your artist's best works) and specialization (learn all you can about one area; work closely with a small number of dealers who handle it.) None of this is new, none of it would have dampened the madness of Evan Connell's connoisseur, and certainly readers who have to be warned against advertised Renoir reproductions at $450 per, or informed that Anuszkiewicz is ""a contemporary American artist of considerable note,"" will need more than the recommended few weeks to become ""experts"" in their chosen specialties. Still, and even though a more cautionary approach might better serve Blodgett's inexperienced audience, he does cover the ground that had better be familiar to anyone with ideas about picking the winners at Parke Bernet.