I've only been practicing Aikido for about eight months. In that time, I've gone to two seminars and ASU's Summer Camp in Washington D.C. I'm planning on attending at least one more this year.
Once I have more experience, I can see myself going to a half dozen or so a year. Right now, I take advantage of being outside Washington, D.C. and being close to Aikido Shobukan Dojo, which means that the annual Cherry Blossom Seminar and ASU Summer Camp are local, as well as a seminar in the Fall. The style is the same and there are enough familiar faces.
I went to my first seminar after just four days of training. It was a "Beginner's Seminar" by Saotome Sensei ("for beginners and those who train them"). There was at least one person there with even less experience than myself. While I don't know if anything I learned there made an impact on my technique, a lot fo what Saotome Sensei said struck a chord.