You don't have to be a CTC member, at least part of the idea of the FNRttCs is to encourage people who have never ridden in a group, or ridden that far, to try it out.
I think if you regularly do the FNRttC, it would be considered nice if you joined the CTC, since at a minimum it's helping with things like insurance for the ride leader (aka Simon / dellzegg).
I'm not mad enough to do the Dun Run, although it's mainly the getting back which puts me off. One year I'm going to organise things so I can collapse in a tent when I get there, but I didn't get things sorted this year, so I'll be doing the slow ride to Brighton thing instead.
Since I'll have gears on my bike for once, I should be able to get up the Beacon without stopping!