Everything old is new again -- at least that's what collectors hope. And the collectibles market is likely to grow as a graying America craves nostalgia.

"Lucky for the new investor that interesting things go obsolete faster, so they become collectible faster too. You don't have to wait 100 years for a wooden-box telephone to be worth something," says Denny Daniel, curator of The Museum of Interesting Things, a Manhattan-based traveling exhibition.

The trick? Determining what will be in demand. "You can find amazing stuff at yard sales, junk stores and on the side of the curb," says Pablo Solomon, an artist and designer in Austin, Texas, who comes from a family of collectors.

Do your research. "Educate yourself on the terms, history and marketplace dynamics," says Stephen Fishler of Metropolis Collectibles & ComicConnect Corp. in Manhattan.

There is no allocation model for this asset class; it's personal, says Bradley Goddard, vice president at PNC Wealth Management in Sarasota, Florida.

Expect fun and maybe profit. Sure, you might make a killing, but mostly, "Assume you will get 25 percent of what you paid, and it will take you three times longer to sell it than you think," Goddard says.

advertisement | advertise on newsday

Items in mint condition command top dollar. If you have stadium seats, don't use them as seats in your living room, says Laura Murphy, fine art specialist with Chubb Group of Insurance Companies in Manhattan.

Realize, much like the stock market, there's no guarantee. Goddard says, "Collect what you truly enjoy and want in your home. Financial gain is icing on the cake."