I have the Good Sam Extended Service Plan (ESP), which will expire soon, and I don't plan to renew it.
My class C has been in the shop several times, and the ESP has covered almost nothing. Most of my problems have been structural -- front cap separation, slideout issues, sliding door tracks ripping out of ceiling, storage compartments leaking, etc. Plus some smaller issues like window blinds failing. The ESP didn't cover any of these things.
The ESP covers equipment like the fridge, furnace, water heater, etc., but not the structural issues. My fridge failed once, but I fixed it myself with a new temperature sensor. I've also replaced a failed induction cooktop and repaired the microwave (blown internal fuse). If a mechanical or electrical component fails, I prefer to get the parts and fix it myself if I can, since it can take months to get an RV service appointment and I don't want my RV to be out of commission while I wait.
So for me personally, the Good Sam ESP has not been worth it.