I just got a KOA card because I had a trip to a KOA planned. After paying for the membership, I still saved another $26.00. It turns out I will use it for a second stay this summer, saving another $40.00. I will likely not renew next year, because I do not live (or travel often) in the US.
I have also had the Camping World membership, used it for a discount on a few items and ended up saving a few bucks in the end. I did not renew this.
I have no problem providing my email address used for spam to save a few bucks...