Back in October, over at the Saverocity Observation Deck podcast Joe Cheung interviewed Noah from Money Metagame and they discussed a post Noah wrote last year asking the question, "Is Anyone Actually Saving Money By Travel Hacking?"
Read the whole piece, as they say, but rather than respond directly to him, I am going to be more proactive and explain how how you really can save money using the tools of travel hacking.
Money doesn't funge itself
Perhaps after opportunity cost, the fungibility of money is one of the most popular concepts from economics applied to travel hacking. If money is fungible, then it doesn't matter how you earn income: whether from employment, reselling, manufactured spending, or high-stakes poker, every dollar you earn goes into the same pot, out of which you make decisions about consumption and savings.
This is true as a description of money, but need not be true about your own behavior towards money.
Ringfence your profits
One way to turn your travel hacking into asset-building is to identify and isolate your profits from travel hacking and direct them exclusively towards long-term asset accumulation. For example, if you have a Fidelity Visa Signature card earning 2% cash back, you're already depositing your cash back each month into a Fidelity account. Instead of withdrawing it into your regular checking account, where it will funge with all your other money, put it into a separate account (I personally use a Consumers Credit Union Free Rewards Checking account that pays 3.09%+ APY).
The key point is that it has to be additive. If you already have an IRA housed with Fidelity that you would max out each year anyway, you aren't increasing your savings by depositing cash back rewards into it, you're just changing the funding stream. Instead, you could open a brokerage account and use your cash back rewards to fund investments in that account.
Buy travel from yourself (with a friends and family discount)
When I'm booking travel for other people, I normally charge them either the cash value of the points I redeem or the fairest price I can think of, for example one cent per mile for airline miles and half a cent for Hilton Honors points. Since in virtually all cases I would rather have money than miles and points, this is usually a way to get my friends and family big discounts and turn my stagnant balances into cash — a win-win.
I don't pay myself for travel I redeem on my own behalf, but you could! After all, if you treat a 25,000-point Hyatt redemption as "free," instead of costing as it does $250 in transferred Ultimate Rewards points, you might travel more than you really, objectively speaking, can afford to. If you instead sold travel to yourself (with the same friends and family discount you'd give anyone else) and moved money permanently into an investment account or other place you were sure you wouldn't spend it, you might develop a more tangible sense of the costs of your "free" travel.
A related issue arises when you redeem bank points like those earned with the BankAmericard Travel Rewards card, Capital One Venture, or Barclaycard Arrival+ against travel purchases: the redemption really does reduce your outstanding credit card balance, and so is clearly some form of "income," but you never actually see a deposit into a bank account. Instead, you simply don't pay off part of the credit card balance you incurred booking your travel. "Buying" travel from yourself is a way of dealing with this curious situation and converting hypothetical profits into long-term assets.
Liquidate into your net worth, not your bank account
I've written before about using Plastiq to liquidate tiny-denomination prepaid debit cards, like the balances left over on 5% Back Visa Simon Giftcards (you can find my personal referral link on my Support the Site! page). Plastiq has a lot of billers in its database, so you might be tempted to use it to pay monthly recurring bills, like your rent or utilities. But making those types of payments won't help you accumulate assets, they just leave extra cash in your already-funged checking account.
Instead, you could deliberately target those payments towards long-term debt reduction, like making additional payments towards your mortgage, auto loans, or student debt. That way, instead of replacing payments you are already making anyway, you're using travel hacking to pay down those debts more aggressively and both increase your net worth and reduce the interest you'll pay over the life of the loans.
The economics professors in my audience are welcome to tut-tut me for suggesting such degrading psychological tricks, but it seems crystal clear to me that if you don't use one of these or some other method of isolating and investing your profits from travel hacking, then it's exceedingly unlikely to actually improve your overall financial position. On the flip side, a few additional thousands of dollars invested in sensible low-cost index funds have the potential to turn your short-term travel hacking profits into long-term financial success.