It's always good to pick it up when they run the discount specials, and if you wait long enough to renew at the last moment they entice with better and better deals. I did a one-day stacker renewal special where I re-up'ed GS Roadside Assistance and GS Club membership for 3 years at a TREMENDOUS discount, and all 3 years paid for themselves when I needed to have my former daily driver towed after grenading the rear differential!
The rate discount is nice when staying for just a couple nights at participating campgrounds, but the real advantage for me is the gas discount because my local station is a Pilot truck stop and I have a 8.1L SUV and a 5.7L Hemi pickup to feed!
While you can find most everything CW sells online for less, when you have a CW 15 minutes from your house it's good to walk in and get what you need without waiting for it.