2. Never value your points or miles at an amount greater than you can buy them at.
I have a joke: What's the value of a FF mile? One? Who wants one mile? I won't pay anything for a mile. Now, if you've got 150,000 let's talk.
One problem with this particular upper limit on mile value that you mention is that you generally can't buy unlimited (or even significant) amounts of miles from a particular program. If I could outright buy 135,000 miles from AA every year, you're right, I really couldn't value them at the list price of an F ticket to Asia. But I can't outright buy that many miles. So does that still mean that the most 135,000 AA miles are worth is 135,000 * $0.035? I'm not so sure.