I think it's a great idea. I don't know if the riding clubs you are talking about are the same as horsemen's associations but I'm guessing they are.
We belong to two. In one of them, we just go to the shows four times a year and get the newsletters. In the other, we take an active part, meetings, rides, etc. It's a good way to meet people with the same interests, learn new things, and have someone to ride with.
I'm supposed to draw up a flier to post this weekend.