I always like to factor in value when using miles. The last 4 years, (we go every May/June) I have started scouting tickets in January'ish time frame and have scored First/Biz seats for only $100-200 more than the economy tickets. We always just purchased coach and used upgrade stickers but found it more economical to just buy FC in the first place. In my view, paying $700-800 for a FC seat is a better value than burning all the miles it would take to secure those seats. An even worse use is using the miles to upgrade from economy if you can book the FC at only $100-200 more. The amount of miles you use will have a much greater value than <$200. Just my two cents.