I went through Dulles yesterday, coming in from a Polaris flight. The Polaris Club was packed as was the United Club. I am SA Gold. There's the first reason for never paying for a membership. The second reason for me is that I am single and resent the whole 1960s family approach. Parents + kids aren't helping the crowding at all.
If it mattered to United, they would spread out the flights instead of banking them.
The United Club at LHR seems nicer to me than anything Polaris and the A club at DIA is a fave since it's my home airport. (Don't bother doing the whole DEN thing - I've lived here since 1985 and won't be changing how I refer to the airport