Here's a Gnarled thought.
Do we use plants or do they use us? For example, we've moved plants all around the world because they had certain qualities that we found usefull. The potato,corn,apple and even psycoactive plants have traveled around the globe. To achieve this they created certain qualities that we found suitable to our needs. Since the apparent purpose of life is reproduction, It seems we're fulfilling that goal.
I would argue the same could be said of bonsai. We literally extend the life of the plant 2-3 times the normal limit. In theory, giving it a much longer time to grow and possibly reproduce. We also move these plants out and beyond their natural borders. Thus, exposing them to new ecosystems.
Perhaps in a way we could be used by bonsai much like other plants appeal to us to satisfy their needs. However, I believe in this case it's like a mutual dependence upon each other. We need them and they need us.