Yes I do. You can never learn everything there is to know about horses. My trainer has been there done that and can teach me something new/more advanced everytime I have a lesson
^^If there was that kind of trainer where I board, I would certainly have one. Because they can help you with things that you cannot really see when you're on their back.
True, I would only use a trainer for something I needed them desperately for, but I like to take pride in my work. Also like you said, you don't know everything about horses, and neither does a trainer, yes, they may know more, but not everything.
I worked with a trainer last summer. I learned what I could from him, and am currently working on my own until I perfect what I learned. At that point, I would like to learn what I can from another trainer, and so on. :)