It's worth it for me if I see a couple things a year. Maybe one or two Broadway shows and then a random assortment of things that wouldn't be on other discount sites. I haven't done the math on your shows but maybe take a look at the rush offers and see what ends up being a better deal.
I've been a member for about five years now and have actually never used it or taken advantage of the benefits. I live in San Francisco so only have to pay $12 for a national membership. I treat this as a charitable donation because I want to support live theater in my own small way.