I was in Pony Club for years, I think it's a great club. I really enjoyed the theory part of it, the manuals are great. As for riding the events are fun, I loved testing, our Pony Club would put on a show every year and it was great! We also had camps every summer and brought in coaches from around the world and learnt a lot, and met tons of new horsey friends.
It's a great thing to be apart of, unfortantly politics between the parents ended up ruining the fun for everyone in my club!
As for wanting to be in eventing, Pony Club is a great for that, the Ridden Tests include Show Jumping, Dressage, and Cross-Country.