If you are so inclined, there's a way to program a formula into a spreadsheet to compare flights.

P = the price of the ticket
M = the miles you would earn from flying on a paid ticket
F = the frequent flyer miles that would be required to purchase the ticket
V = the value you place on each frequent flyer mile

The "adjusted cost" of a paid ticket is P - (M*V)
The "dollar equivalent" of a mileage ticket is: F*V

For example, a flight from NRT to SFO is 5124 miles, as a platinum a total of 20498 miles earned on the round-trip, next week the cost is about $1000.

So, adjusted cost, using 2 cents for mile value, adjusted value is 1000 - (.02*20498) or 1000 - 409.96, or $590.04.

With miles (assuming low award available) it would be 60,000 * .02 or $1200.

So, if you value the miles at 2 cents, even in the unlikely event that you can find a low award, you should buy this ticket with cash. This is true even without considering the value of making progress toward your elite qualification.

You can program your spreadsheet and just plug in the values to make comparisons. It probably seems like a crazy thing to most people, but I find it helpful.