Paying extra really sucks, but I'll do whatever it takes to get an aisle seat. The middle seat is HELL (espcially when you're big & tall). No armrest priviledges.
I recently got stuck w/a middle seat (after being rebooked, so I had no choice) and it was awful. Once the seat belt light went off I got up and stood for 2 1/2 hours (sometimes the flight attendants won't let you do this, but I had a sympathetic FA on my flight).
Flying has become this hellish gauntlet you have to endure to get to your destination, and it's only going to get worse. Yippee!