We have memberships with Good Sam and KOA. They pay for themselves fairly quickly after a few nights. However, weekly and longer rates are almost always lower than the discounted nightly rate. But sometimes a combination of weekly and nightly can be used when not staying an exact multiple of 7 nights. They are also good for overnight stays while traveling.
We've looked into Thousand Trails, but it seems you have to use them a LOT for it to make sense and we don't want to base our locations around Thousand Trails locations. Additionally, the few times we've stayed at a Thousand Trails park by coincidence, they have not been the nicest parks.
Our friends Jason and Rae (Getaway Couple) have a few videos in favor of Thousand Trails: www.youtube.com/results?search_query=getaway+couple+thouseand+trails
And, our friends Phil and Stacy (You, Me & the RV) have this one against: youtu.be/5zQxKYDD2OQ