From duck decoys and hood ornaments to limited-edition sneakers and Pez candy dispensers, offbeat collectibles attract the eye of investors who crave tangible assets they can appeciate and that ... well, appreciate in value. Assembling a collection of rare items is as much a labor of love as an investment tactic and won't necessarily net owners significant returns. Then again, it might.

"In general, these are considered speculative types of investments," said Russ Robertson, a certified financial planner with WealthCrest Financial Services. "You can get great returns, but it comes with high risk, unless you really know what you're doing."

Pez aficionado Dale Pike of Pittsfield, Mass., who has amassed more than 1,000 of the themed candy dispensers over several decades, estimates his collection might fetch only about $5,000 if sold. Terry Kovel, co-author of "Kovels' Antiques and Collectibles Price Guide," said market oversupply has depressed Pez prices recently. However, a single Pez dispenser was recently sold on eBay for $499.95.

—By Sarah O'Brien and CNBC's Kenneth Kiesnoski.
Posted 4 May 2014

Waterfowl decoys are hotly sought-after collectors' items, their value continually rising since the 1960s. In fact, a duck decoy sold in January at Sotheby's in New York for $767,000. It was a male eider created around 1900 by an unknown carver.

Collector Harry T. Williams, of Worton, Md., has built his own "duck dynasty," of sorts. Eight out of three dozen duck decoys he bought for 50 cents apiece about four decades ago are the original core of his collection. While Williams realizes the investment potential of decoys, he does not make purchases for that reason. "I look for what I like," he said, adding that he focuses on local carvers—that is, Maryland-based artists.

The market for collectible sneakers is booming among young adults across the U.S. and abroad. We're not talking smelly gym shoes here; Joe Diorio, owner of Brooklyn, N.Y.-based shoe show SoleXChange, said he saw a pair of Nike Air Mags sell for $6,900 earlier this year. A limited number of Air Mags, based on sneakers Michael J. Fox wore in the "Back to the Future" movie trilogy, were released in 2011.

Diorio's company holds events in various cities, where attendees can buy and sell. On May 4 SoleXChange will be in Philadelphia at Temple University; on May 31 the company will hold an event in Freehold, N.J.

A subculture of automobile aficionados values anything related to cars—from antique chauffeurs' hats and licenses to spark plugs and classic hood ornaments. "Hood ornaments can go for a fortune," said Terry Kovel, co-author of "Kovels' Antiques and Collectibles Price Guide." Indeed, one was listed last month on eBay for $199,999.

They say it takes all kinds, and there's something for everyone. People who are mad about antique electric fans can find company in the Antique Fan Collectors Association, which this July will host what it calls the Fan Fair convention in Indianapolis. According to the 500-member AFCA, the average fan collector has been collecting for 12 years and has 70 fans in his or her collection. Twenty members of the association have been collecting fans for three decades or more.

AFCA treasurer Dick Boswell says that most antique fans can sell for several hundred dollars each. Unique or rare examples can net owners quite a bit more; one such device, Boswell noted, recently fetched $13,200 in an eBay auction.

Collectors of clocks and watches—a tad more common than Pez dispensers and duck decoys—have, of course, their own organization: the National Association of Watch and Clock Collectors, which owns and operates the National Watch & Clock Museum in Columbia, Pa.

Watch and clock collections can really bring in the big bucks and appreciate in value over ... time. Prices paid at auction for the most highly prized timepieces run into the millions of dollars. For example, the one-of-a-kind 18-karat "Henry Graves Supercomplication Watch" from Swiss luxury watchmaker Patek Philippe—designed for banker Henry Graves Jr. back in 1933—was auctioned at Sotheby's in late 1999 for an eye-watering $11 million-plus.

Even vintage condom tins carry value. Condom tins, you say? Yes, at one time prophylactics were sold in fancy metal packaging. Kovel explains that today's collectors are drawn not only to the interesting illustrations on the tins but also the fact that they are no longer made in this throwaway, disposable age.