(MONEY Magazine) – By now you've probably heard the incredible shocker: Superman is dead, bumped off by Doomsday, an underground creature in November's Superman No. 75 comic book. There's even worse news, though. If you were thinking about trying to make money by collecting copies of the Superman No. 75 (retail price: $1.25; $2.50 for a collector's set), forget it. With a print run estimated well into the millions, says the author of the definitive Overstreet Comic Book Price Guide (Avon, $15), Robert Overstreet: ''You can't count on them to appreciate at all.'' Still, speculators can put Pow! in their portfolios by joining the half a million collectors who invest in older comics today, up from a few thousand hobbyists 20 years ago. Even the swank Sotheby's and Christie's auction houses recently have been selling the books. The comics with the greatest potential for appreciation are collectibles published in the '50s and '60s that baby boomers crave to relive their childhoods. Current price range at dealers: $22 for, say, a 1968 Amazing Spider-Man No. 61 in near-mint condition, to $5,500 for a gem like 1956's Showcase No. 4, which marked the first appearance of The Flash. Despite a hot market that has driven up the prices of the most valuable of these collectibles by more than 50% annualized in the past five years, Maggie Thompson, co-editor of the weekly Comics Buyer's Guide ($33.95 a year; Krause Publications, 700 E. State St., Iola, Wis. 54990), believes they'll probably appreciate at twice the inflation rate during the next few years. For the greatest chance of appreciation, buy the best-quality book you can afford. ''A comic book in near-mint condition is generally worth at least seven times more than the same one that is creased or discolored,'' says James Payette, a dealer in Bethlehem, N.H.