To clarify, I don't do studio portraits. I do everything on location, and typically they are unusual ones. I would not enjoy maintaining a studio and shooting there day in and day out. Also, I think there's a difference between a portrait and an image with a person in it. I don't think of most of my gallery work as being at all portrait-like.
As far as the value of being in a gallery, it's about exposure for me. The more people in my target market who see my work in a positive, fine art setting, the more potential portrait clients I have. (Forgive the poorly constructed sentence there. It's late.)