What it comes down to for me is that the domestic F product just isn't worth that much, compared to what I could otherwise get with the miles (international tickets). I think have UG'd with miles twice domestically, once for PVD-HNL, which is so long that the larger seat is worth it, along with the then-better F service on Hawaii flights, and once for a transcon on a 3-class plane (with a hot meal), with a connecting flight.

I don't see springing for the co-pay very often.