Might as well go back to the concept that it's all individual and that the critical point is "how much you would have otherwise personally been willing to pay for the same trip". That's the simplest way to evaluate, and it varies from person to person.

Factors that go into this include your current personal financial situation, your current point balance, your rate of incoming points, how close you are to the next status level, your willingness to take funky flights to spend less $$ or earn more points, the premium you're personally willing to pay for FC or BC seats, etc.

In my case, I used to travel a lot for business, but recently got out of consulting and mostly travel for vacations and holidays a few times a year. I have a few hundred thousand miles, but am not earning many now. I'm doing ok financially, but not so well that I wouldn't rather spend the points when I can get a "good deal". I started this discussion to try to define the threshold for a "good deal", and I think I'm comfortable that for me, that's somewhere around $0.0125.

I suspect that the majority of people out there would evaluate their threshold somewhere in the 1 - 1.5 cent range when pushed to not evaluate their FC seats at the airlines' rates. The exceptions are:

1 People who fly so infrequently that they're better off using the points as soon as they have enough (MileKing's scenario). For these people, point value is not very relevant.

2 People who earn points so fast on business travel that they can't spend them on their demand for personal travel fast enough. For these people, point value is not relevant. This was the case I was tring to make that MileKing disagreed with, but I think it's still true if your point balance and earning rate exceed your personal demand by enough.

3 People who's point balance and earning rate are out of proportion to their financial balance and earning rate. For these people, point value may still be relevant, but not evaluated at the same exchange rate. For example, if you have 500,000 miles and you get fired, you're likely to spend your points on any necessary personal travel where the cash alternative isn't super-cheap (say, a rate of 0.6 cents/point) until you can get a new job.

I guess point #3 may also explain the variation among people who aren't at extremes either (those that would evaluate between 1 cent and 1.5 cents). My point balance is a bit high for my financial standing, so I might be willing to take a flight at 1.15 cents at the moment.

MileKing wants 1.32 even though he has 3 million miles, so clearly he's loaded financially. Kidding.