1) The first step in evaluating whether a mileage run makes sense is determining the value of miles for you. The critical error to avoid here is simply assigning what an award costs, not what it's worth to you or what you'd pay for it.

If you intend to use your trips primarily for first class trips to Greece, and those trips cost $20,000, you shouldn't jump to use this figure to determine the value of your miles without pausing to think. What is the trip worth to you, would you have actually paid this figure for that ticket? You don't want to spend $15,000 worth of effort thinking you are getting a good deal for something that is really only worth $3000 to you. There may be some benefits of award travel tickets over purchased tickets you should consider, like free stopovers.

Don't ever forget that miles most certainly will depreciate in value over time as awards become less available, have more restrictions, or cost more miles. If you won't use your miles for many years, maybe it's not worth killing yourself for something that could well be worth very little someday. Airlines have every right to change their program however they like, and are required by law to do whatever maximizes shareholder value... No mercy! More airlines are sure to go bankrupt. While miles historically have miraculously survived bankruptcies (TWA, etc..), there are no promises for the future.

2) Once you have a value of miles, you can factor in the double miles you'd get for future travel on higher elite status. You could assign a value for the other benefits of elite status and factor it in -- free upgrades every 10,000 miles, special elite lines, club use for international travel, that really pretty card that impresses vacuous people. Anyway, you'll get a dollar estimate for how much each tier is worth to you.

3) When evaluating a mileage run, factor in the cost of airport transportation or parking, and any hotel costs. Finding cheaper hotel rates can help you justify much more travel. Far more importantly, how much is your time worth to you? If you get little enjoyment out of the run itself, time is money, and you're flushing it.

If a 4th connecting city only gets you 45 extra miles and flushes 3 additional hours, consider taking a slightly more direct route on the run! I see this mistake all the time. If you extend the stay of a mileage run and see friends or enjoy exploring new places, it may be far easier to justify the run that is now a mini-vacation...

I almost always turn my mileage runs into travel runs, visiting new places or friends, even if only for a few days. It's incredible how much you can do with 2 days in Manhattan, Hong Kong, Buenos Aires, etc... ****, everyone should go to Buenos Aires right now.

Anyway, either I keep an eye out for cheap fares for places I'd like to visit, or an unusual fare gives me a new idea to explore a place I hadn't considered. A person with little free time would have a harder time justifying a pure mileage run, because their limited time would be more valueable. If your run alienates or stresses people you care about, don't forget to factor that in. Again, always consider what good you could have gotten elsewhere out of alternate uses of that same time.

4) Steps 1,2 and 3 are important, because they indirectly determine how much time and effort is sensible for each mile. It will be different for each person. Now pause to consider opportunity costs -- what could you have done with that same time and money? Dollars are really abstract figures, and it's easy to lose sight of how much they are really worth to you. Stop and think about something you value, but don't buy as much of as you'd like because of cost. Say visiting someone you care about costs $1000 per trip.

Then instead of using an abstract dollar amount to determine if something is worth it or not, you can instead say, "Is this worth 2 trips to visit sally? The cost of this item could have paid for half a trip, is it really worth that much to me?"

5) Another angle to check the value of something is to consider the amount of "economic slavery" required. Suppose an optional car purchase eats up a full year of your *discretionary* spending (do not use gross earnings for this step!) Then you'd pause to consider, is this car worth a full year of working day after day, with nothing else to show for my hard work? A person who enjoys cars much more than someone else, could justify more work days flushed to getting it. This makes you think what something is worth to you, not what the dollar cost is.

I'll edit this and add more later perhaps.