We belong to C2C and have been happy with it although we don't get to travel anywhere near as much as we would like to. Our home campground is very well maintained and has nice amenities. The campgrounds we have visited have also been well maintained. I know this isn't much info but I hope it helps.
Sorry I don't even know what RPI is. I did get the deluxe C2C membership and frankly I don't have enough time to use all those benefits. If the RPI membership equates to more campsite availability it's probably worth the $65, especially if you plan to travel extensively.
We have been members of C2C and RPI for quite a few years. There is a lot of overlap between the two. We often would use the RPI membership when a park was both just because we didn't need to use the "Green" cards and could just pay cash instead. Now however, C2C has done away with the green cards and converted them to a point system. The jury is still out on that for me - not sure how it is going to work for both the member and the campground. There have been times where there was only an RPI or only a C2C campground where we wanted to go however, so the dual membership has worked out for us. You might check out my reply on the thread "Campground Memberships" earlier.