I'd pay for the extra seat. I fly IAH-SNA quite often. When its reasonable, I buy a P or A fare. Usually around $1100. However, sometimes it can be $1600.
A typical coach fare is $400. I'd be willing to pay an extra $400 for the extra comfort and space.
Its all personal preference. I am a big guy (not fat)... 6'3" 275lbs. built like a lineman. having the extra width of the empty middle seat makes all the difference in the world.