I just flew LAX-IAD red-eye. I debated this similarly, but I decided I'd be sleeping the entire flight. I can sleep fine in coach/exit row so I neglected to upgrade. I think red-eyes are generally tough to upgrade though so don't count your chickens just yet...
To me, 5-6 500-mile upgrades isn't worth it if I'm going to sleep the entire flight. However, for those who can't sleep, or can only sleep with the added pitch in F, then I think it'd be absolutely worth it; just depends on each person. For me, I wouldn't, but I have no problem sleeping on flights regardless of seat.