Before you decide, make sure you know what you are getting, otherwise you will spend money on something you never use.
I agree with OP that KOAs are overrated and overpriced, but if they suit you, a membership could be worthwhile.
I found Passport America a good enough value that I signed up for ten years to get a substantial discount. But you should understand that there are many different kinds of member parks. Some are residential parks that set aside a few spots for RVs, and some are resorts, but probably will not give you the discount on weekends, or during their peak season.
Good Sam on the other hand is a completely different animal. You only get about a 10% discount, but you get the peace of mind that someone from Good Sam has inspected the park, and a reasonable quality can usually be assured. In addition you can get discounts at Camping World, and other places.
If you are over 62, you should get the Park Service All Access pass which gives you 50% on NPS and COE campsites. It is $10 for life.