This question comes up all the time. The membership park systems are great if you use them extensively and a financial burden if you don't. The key is that you are making a long term contractual commitment to get the reduced cost camping. If you aren't sure you will go to the parks often enough to make it worthwhile, don't even consider doing it.
We know folks who spend dozens of nights/year in membership parks and love them. Others bought in without much forethought and then found they wanted to go elsewhere instead, but were stuck with a long term contract. There are also any number of folks who basically use just one park as their summer home and enjoy having the same neighbors and regular social events at their membership park. Different strokes for different folks.
If you do decide to buy into a park system, buy on the resale market rather than direct. Cost savings are often huge, as much as 80% in some cases.