Personally, I would never even consider booking award tix in C... for the simple reason that F is not that much more than C, comparatively speaking. For instance the difference between a C and F award ticket to Japan is only 15K miles each way. And who wouldn't jump at the chance to upgrade to F to NRT for only 15K miles?!

I've had plenty of opportunities to upgrade to Int'l C with SWU's (that's what they're for!) BUT, since I never envision having enough cash to pay for Int'l F (unless it's a major mistake fare!) I look at F award tix as my only chance to experience International First Class. Even upgrading to F with SWU's is out of the question since the only Biz fares I would pay for are Z fares, which aren't upgradeable.

Furthermore... availability for saver award tix in F are much easier to come by than C. Just as the OP has experienced, for some reason C awards are the hardest to find. And frankly, it's just fun to tell people you flew on an $11,000 airplane ticket.

I went to NRT last year in F with the bf and it was the best 270K miles I ever spent.