This was a great question. I am a new 1k as well after many years as 1P and was wondering the same thing. I am lucky enough to have worked out a deal with my company that any international travel is in C, and based on my experiences in the new C don't see the benefit in using them for an upgrade to F.

Most of my domestic travel is from IAD to West Coast and even though the F is OK, as long as I get my favorite E+/Exit seat I don't mind the Y travel (and I am 6'3").

I have thought about an international trip with mrs. caphck and using them to upgrade that flight, but with two young kids it is hard to find the kind of time you need to really enjoy an international trip.

Guess I will probably use them for an F upgrade on my international trips, but I have this odd feeling that I will get into October and still be sitting on my SWUs and CR-1s.