I'm not a member of my local riding club but have been to a couple of their shows and helped at one. They are really friendly and welcoming. If I had something to ride and transport I would def. go for it.
Being a member doesnt mean you HAVE to attend stuff, you can just go to shows and enjoy.
The cliques only get you if you let them nd i f you are only occasionaly competing and the odd bit of helping out you can stay out of it all without any effort and they are good fun and a great way to meet lots of nice people.
I joined cos my local one, it offers great training - lots of different types and different levels (names at brilliant prices) and a few social things, but you'll get that sort of behaviour in all types of life. I just don't get involved.
There is only one good one near us that offers to do things the rest only hold shows so bit pointless joing those ones if they have loads going on id go for it and enjoy and just ignore the clique if they have one people like that not worth stressing about have fun and good luck what ever you decide!