Now I have to admit that I've never studied the economics in detail. Patching tubes just seems like the right thing to do, and I've always got something that I can do while waiting for the goop to dry.

I carry a tube and a patch kit on each bike. Belt and suspenders. That's always been sufficient for my riding conditions -- no goat head thorns, thank goodness, and no pinch flats. If I change a tube while on the road, I patch the other when when I reach my destination, or at home. I've had success with patching a tube without removing the wheel from the bike, when I knew exactly where the puncture was.