In addition to the dollar cost, there is the time cost. If the flying I normally do for work takes me to 50k+ miles (BIS), and I plan to do a few big international trips the following year, it might be completely worth it financially to expend another $2-3k in trans-pacific mileage runs to reach 1K. However, the time factor needs to be considered, whether that is time away from family, opportunity costs for other earnings, or simply how you value your time. Yes, I could get a lot of work reading and other things done on a plane (without pager, cell phone, etc.), especially in C, but my four year old would be much less understanding about that.

The problem is that once you get into this game, it's very easy to want more! Just a year ago I was thrilled to get 2P, love the 1P benefits this year, and (very surprisingly to me) I catch myself thinking, "Hmmm. How can I convince my wife that doing a MR makes sense to make 1K?"