A lot of that depends on how you value the flights (a lot of the benefit comes from being able to do international business class one way with points very easily, but those tickets being very expensive in cash), but it is pretty straightforward if you both optimize the earning, optimize the spend, and optimize the points programs.
To give you an example, a business class ticket from Seattle to Taipei with EVA (a very nice airline) is about $8000 round trip or $6000 one way. You can book it for 75,000 Aeroplan points one way. That is 1-2 credit card signups.
But Aeroplan also lets you have a stopover in the middle of a trip and lets you string together up to 6 flights and only pay based on the distance.
So you could do Seattle, do a layover in Taipei, have a stopover in Manila, stay a day in Singapore, and then land in Darwin Australia for 92,500. Which is closer to 2 credit cards, but still easily achievable in a month or two. But the value of that trip when I did something similar was closer to $12,000. Prices out at around $9000 for my test dates for the flights I did.
Now, you need to take many trips a year to do that as a single individual (which I am), but the referral streams for credit card signups are also very powerful, so get a Player 2 as it is called, and you can easily get 20-30% more on your signup bonuses and each person can also do the bonus.
And that is just business class. Once you start getting into First Class redemptions (hard to do, but the serious people manage it), the value can easily be the equivalent of a 12K for a simple round trip, yet alone stacking First Class products as many programs let you do.
Some of the pricing is also probably last minute. Points costs fall last minute, but cash prices rise. That boosts your cost per point, or CPP as we call it.