I like the idea of valuing miles based on "cost to acquire", even if that method is imperfect.

One big issue I have with those who think their miles as worth some high number-10 or 15 cents each, for example-because they took (or could have taken) a high cost trip for those miles. The problems with this method are:

1. Using readily available airfares to value miles, the use of which is geatly restricted. For example, using FC fares to Europe to value miles even though you can buy the FC tickets on a walk-up basis, while using miles means you have to plan a long way ahead, and often can't go when you prefer.

2. Ignoring cheaper fares. Example: You could use $7,000 as the cost of business class to Europe since that's the fare on several airlines. But a 50 day advance ticket on CO is less than half of that. Miles would save you the cheaper fare, as that's the one any savvy customer would buy.

3. Present value. Building those miles takes time, and the cash in the bank you could have had would earn interest.

4. Miles devaluation-That risk is there until you get the award.

5. Unused miles-like those green stampes in the kitchen drawer, scattered miles may never be used.