This thread is right on point on what I am trying to figure out - maybe someone here can tell me if my reasoning is right:

Wife and I planning to fly to Japan. Could use 90K/each for a business tik (on UA) OR buy two coach tiks for about $1,600 each and then upgrade to business for 30K/each (need to spend money for the higher class to upgrade).

Hate to spend $3,200 out of pocket but we would then earn miles, which would keep our status up for next year (brings up the question of the value of status, but that is for another thread); save 120,000 miles for use another time; and the miles we would earn, combined with the various promotions at UA, would get us halfway to our upgrade. SO, the way I see it, if you value the 120,000 miles we would save at 1.2 cents or thereabouts, it comes out to almost the cost of one ticket. In effect we would be "spending" $1,600 for two business tiks to Japan. Is this reasoning warped or should I just fork over the 180K miles???