It's more a breakeven point + opportunity cost than a strike price like a stock option. My breakeven is 1.5cpm for AS, so if I don't have conflicting plans I'll probably do a mileage run. And yes, saver fares are cheap but if you're factoring in upgrade chances, given the choice if you would pay the $+20-30 difference for a fare (multiplied by the odds of getting upgraded), I'd say the choice is pretty clear against saver fares. If you're not getting upgraded, then book saver.