$800 for a year? Wow. We don't have anything close to that in our area, but I'm sure it's region dependent.
We have bought many family passes over the years - to children's museums, the science center, etc. They were all bought on discount, usually a steep discount. In my experience, places oftentimes offer discounts on or around Cyber Monday or Black Friday in November. If you don't live in the US, I'm sure your country has equivalent sale periods during the year.
I would like a place on FB, and sometimes they will announce deals via social media.
Sometimes the memberships paid off; sometimes they didn't. This year we have a pass to Six Flags, but since I broke my foot in the spring, we haven't been able to go as often as we wanted. Oh, well.
I agree that the best part of a pass is that you don't feel obligated to spend hours and hours with cranky kids just to feel like you got a good value.