For some a hobby, for some an obsession and for others everything in between. And I think it can be whatever you want it to be. I mean for some it’s intertwined with their career, so hobby may not be the correct term. It should bring a level of enjoyment and positive enhancement to your life I think.. Perhaps we should not try to label it?
Another point of view is that one can loose perspective on the importance of audio or any interest. Once the interest becomes more important than other aspects of life that are clearly more significant and important, spouse, children, friends etc. then I think one has lost perspective in life. What is special, meaningful, spiritual and truly important gets lost.