NEW YORK (CNN/Money) - The words "nudist colony" might conjure up notions of waifs dancing through fields like castoffs from a production of "Hair." But those who do stuff in the buff want to project a different image.

Nudism is trying to dress itself up.

"Nude recreation encompasses an incredibly wide variety of activities," says Judy Ditzler of the Naturist Society, an industry association.

There are nude cruises and motorcycle rallies, clothing-free hiking and camping. A charter airline ran a nude flight, and at least three nudist summer camps for teenagers are in operation.

Most important, there are about 260 clothing-optional resorts in North America, which are responsible for the bulk of spending in the nudity business. That's nearly twice the number of 10 years ago, according to the American Association for Nude Recreation. Many charge top dollar for spa treatments and really fluffy towels.

A relatively affluent customer base has pushed nudism in the U.S. to $400 million in annual revenues, according to the AANR. That's up from $120 million a decade ago.

"Any time somebody can drop a couple of grand on a cruise, you can assume they're at least comfortable financially," says Nancy Tiemann of Bare Necessities, a travel agent in Austin, Tex., that specializes in nudist cruise packages.

In Palm Springs, Calif., Steve Payne, a former manager with Hilton and Sheraton, opened the Desert Shadows Inn in 1992 as an 11-room bed-and-breakfast. Today, it's a 92-room complex, including villas, condominiums, and a spa. Cost for a suite: $2,500 per week, including tax but not sun screen.

In Pasco County, Fla., the $45 million Caliente hotel and condominium recently opened. You can play tennis, volleyball, and shuffleboard -- while letting it all hang out. It is one of 6 nudist resorts in the county.

"These are mainstream properties, with common pools, landscaping, roads and the kinds of amenities you'd see at any other upscale development," says Hugh Lichter, vice president of Diversified Mortgage in Clearwater, Fla. One of them is even next to a Wal-Mart.

Lichter is not a nudist, but he has written loans both to developers and individual property owners in the Pasco County nudist community. He says prices for building lots in nudist developments in Pasco exceed the cost of similar lots nearby.

Third-of-an acre lots in nudist developments have recently sold for between $80,000 and $110,000, according to Lichter. "The same lot up the road would cost between $45,000 and $50,000," says the lender.

Mindful of such numbers, some public officials promote nude recreation as just another element of the local tourist trade.

When the Desert Shadows built a foot bridge to connect two parts of its property last year, the city of Palm Springs kicked in $185,000 to make nearby road improvements. The county also granted Payne a variance for a liquor license (a law aimed at strip clubs had been a hindrance).

In Florida, according to the AANR's Carolyn Hawkins, the Pasco County Chamber of Commerce holds regular get-togethers at nude clubs that attract as many as 300 (clothed) guests.

Nudists are careful to stay on message -- "no sex please, we're naked" -- and tend to speak from the same page when promoting their avocation.

The benefit of a nude beach? No sand in your suit, three said in separate interviews.

Two sources stressed that when you're naked, class distinctions disappear. "You can't tell the difference between an attorney and a bus driver when they're not wearing clothes," one said, without even chuckling at a lawyer joke made in response.

Boosterism aside, few would dispute that nudism's a niche.

According to the Travel Industry Association, Americans spent $455 billion on travel and tourism last year. Camping alone is a $7 billion business, notes Cathy Keefe of the TIA.

Measured against that, nude recreation is barely a rounding error. Even so, cruise packager Tiemann's experience may be instructive.

Bare Necessities started out 12 years ago selling cruises on boats with a few hundred passengers. Now, the business is a mix of high-margin small groups and mass-market trips.

Last year, Carnival Cruises, which operates the ships as charters, told Tiemann that a smaller vessel would be unavailable for a planned cruise. So she had a sudden sales challenge to fill many more berths on a bigger-than-expected ship.

She marketed the trip in the nudist press and mainstream travel magazines owned by Conde Nast. Result: 2,000 naked passengers on one of the largest, ahem, "bareback" cruises ever. (Carnival's Jennifer De La Cruz confirmed the number.)

Not only did the boat sell out, says Tiemann, "there was a waiting list."

Bare Necessities is organizing an even larger cruise for next year.