I received the spend-$500-get-10000-points, spend-another-$4500-get-5000-more points offer. Strangely, the offer implies that this activity will generate enough points to earn a free flight.

However, I am in the program that earns 1 point for every $2 spent. By my calculations, a $5,000 total spend will generate 2,500 regular points + 10,000 first bonus points + 5,000 second bonus points. That totals 17,500 points, not 20,000 points needed to earn a free flight.

I'm probably going to go ahead and take advantage of the initial bonuses, even if I have to spend $10,000 to get to 20,000 points. That still is a potential 4% return ($400 ticket / $10,000 spend) on a airline ticket that will earn miles. On top of that, if I hurry up and double dip on the NW miles until the middle of June, that's another 0.5% return if you assume that NW miles are worth $0.01 per mile.