I don't think AC memberships provide value. If you have an overabundance of miles, it might be worth it, as Admirals Clubs tend to be a bit quieter than the terminal, but the ROI on the $3-400 you would spend is ridiculously low. For the same price you could get 100 lattes at your local starbucks.
Additionally, I've found my AC membership to be worth even less lately as everyone seems to show up early and camp out in the club. The last two weeks, I've had trouble finding a seat in Dallas, and Chicago clubs.
For my money, you're better off checking in at the first class counter, buying a double espresso, and picking up a paperback at the news stand. You'll spend less if you only travel once per month and you're overall flight experience will be improved.