I'm a leisure traveller who does 50K+ a year in domestic travel each of the past few years. All of that travel has been on United and I don't mind one bit paying $50-100 more to fly them over, say, Southwest.

I use my miles exclusively for upgrades. The first exception was this year on a trip to GSO. I could not get into North Carolina for less than $500, so I coughed up 25K for a saver award and was even given a free upgrade to First ORD-SEA.

Since I fly leisure, and I always need a car, I have the luxury of being able to fly 200 miles near to my destination to get a better fare and then drive. I can often save hundreds, which then pays for the rental and much of the rest of the trip.

And then their is status. Bypassing the humongous waits at SEA to use Elite Security alone makes spending the extra time and money to be an elite worth it.