Take the F route. No question.

If you or your wife are approaching a particular status level and need the miles, there are numerous great MR opportunities out there right now. Why not accrue the necessary miles for each of you (at a much lower cost than your option 2) on a MR or two and splurge in F for your long trip to SA.

Put another way, what good are miles if you feel guilty using them? I fly enough to manage 1P each year (1K is really not a possibility) and also redeem miles 2-3x each year on domestic trips where fares are expensive but saver Y seats are available. The value of miles is only going down - best to use them when you can!