It's an investment up front, but my kids love it. I am not crazy about spending all day in the sun, but with a pass I can justify an hour or two at a time four or five times a week. When we pay per visit, I feel like we have to spend five or six hours to get our money's worth. Todd loves the water and will take them for longer stretches when we are here on weekends.
Bonus: everybody is happy, I get a little time alone on weekends, and maybe I will finish Essays by EB White, which has been on the nightstands for months.