Even novice players of the airline mileage-program game know how to earn extra frequent flier miles through shopping, dining, hotel stays and car rentals.

Now there’s one more way to feather the free-trip nest: On Monday, United Continental Holdings launched the MileagePlus Gift Card Exchange, a program that allows members of United and Continental airlines’ MileagePlus program to swap unwanted gift cards from more than 60 major retailers for miles.

“The program enables members to get value out of gift cards that they normally wouldn't use or didn't want,” said United spokesperson Charles Hobart. The airline claims the program is the “first of its kind.”

To swap cards, MileagePlus members log into their accounts and enter the value and other information from an unwanted gift card. The site will verify the card, make an exchange offer in miles and, if the offer is accepted, "take" the card and, within about five days, deposit miles in a member’s account.

There are some restrictions: Cards with balances below $25 will not qualify, nor will cards that have expiration dates. And not all cards will be accepted or exchanged for face value. “Our rates are determined by market pricing, which is affected by several factors,” the program rules state. Those factors determining a card's value aren’t fully spelled out and the rules note that the mileage offer displayed for the same gift may fluctuate over time.

 “This looks like a modest win for MileagePlus members, who now have yet another option for using their miles,” said Tim Winship, publisher of FrequentFlier.com, a site about airline-mileage programs. “But without a set exchange rate when converting card balances into frequent flier miles, it's impossible to assess the real value of such exchanges except on a case-by-case basis.”

Winship says that floating exchange rates will likely detract from the new feature's popularity, as could the 7.5 percent federal excise tax he suspects will show up as a reduction in the number of miles members receive for any exchange.

“If the exchange rates are generous enough, the tax hit may not matter,” said Winship. “But for those drawn to the program for its convenience, it's probably a non-issue” and will likely be a feature other airlines and hotels may soon add to their programs.

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They say money can’t buy you happiness, but when it comes to air travel, it can buy you the next best thing: the frequent flier miles you need to get award seats, upgrades and access to the once-exclusive world of elite-level flying.

The question is how much are you willing to spend and how much are those perks really worth?

“You have to be smart about it,” said Tim Winship, publisher of frequentflier.com. “You need to make sure you’re going to recoup the cost of what you paid for them.”

For the average traveler, that means buying miles or points in order to reach a threshold for an award ticket. Most airlines charge 3 to 5 cents per mile, although several are currently offering deals to entice mile-shy shoppers. Through Dec. 31, for example, US Airways is offering a double-mile promotion that brings the cost down to 1.75 cents per mile.

But even that is higher than the generally accepted value of miles, which Winship pegs at around 1.2 cents each. (By that reckoning, a 25,000-mile award seat is equivalent to a $300 fare vs. $437.50 at 1.75 cents per mile.) “Unless you know you’re going to redeem those miles for a ticket that’s worth what you paid for the miles, or hopefully more, you’ll be overpaying,” he told msnbc.com.

For more frequent travelers, however, the issue isn’t award tickets but rather membership in an airline’s elite-status program, which, as the commercial says, has its privileges. Travel with your preferred carrier enough during the calendar year and you’re rewarded with perks that can include priority screening and boarding, priority or complimentary upgrades and the waiver of à la carte fees.

Historically, the only way to achieve elite-level status was to fly a lot — at least 25,000 miles per year in most programs. Come December, fliers shy of their desired status level would embark on “mileage runs,” masochistic endeavors involving multiple flights, long distances and short turnarounds in order to ensure their membership for another year.

Over the last few years, however, the airlines have figured out that fliers anxious to retain their perks get even more so as the clock ticks toward Dec. 31. Instead of forcing them to take that one-day trip to Timbuktu, many carriers are letting them pay for the privilege instead.

“It can be a good thing for fliers because it gives them an option,” said Brian Kelly, founder of the ThePointsGuy.com. “It’s not a cheap option, but it is an option nonetheless.”

How “not cheap?” On US Airways, travelers can purchase up to 4,999 Preferred miles for $399, which works out to 8 cents per mile. Delta, meanwhile, is running a promotion through Dec. 15 in which travelers can buy Medallion-qualifying miles for 9 to 12 cents per mile. And Continental’s Elite Maximizer program uses a sliding scale in which the cost climbs as the status-clock winds down.

“The price depends on how desperate they think you are,” said Kelly. “Toward the end of the year, it can cost 20 cents or more per mile.”

Whether buying elite qualifying miles is a good deal, especially this time of year, requires a complicated calculus that weighs the out-of-pocket cost with the dollar cost of a ticket (pricey this time of year), the value of your time and your tolerance for packed planes, lousy weather and the other hazards of late-December travel.

“You need to be clear in your mind about what the real value of elite status is to you,” said Winship. “If you’re not flying six roundtrips a year or more, I’d question the rationality of paying extra for it.”

On the other hand, he adds, “If you’re at 23,000 miles, it can make sense to buy a couple thousand miles to get you over the hump.”

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Rob Lovitt is a longtime travel writer who still believes the journey is as important as the destination. Follow him at Twitter.