I'll use my wife's miles for the kids to fly domestic coach at around 1.6 to 2 cents per mile. That's because she doesn't earn enough miles to get us overseas in business. I save mine for the two of us to fly international business class, usually works out to around 5 cents per mile. Personally I don't think that F is worth the extra miles at all, but that's a matter of preference (I might do F for our celebratory retirement trip to Australia).

My wife has no status to maintain, however if this was a problem then I'd be slightly more willing to buy a ticket and so would like a (slightly) higher value before using miles domestically.