Ander,
you bring up some valid concerns; concerns which many of us have mulled over. I've concluded that whether it's obsessive or not, it's who we are. Some people are sports fans, news junkies, gear heads, workaholics, wine connoisseurs, and more. I think that having a strong interest in any area, as long as it is at least morally neutral, is one of the wholesome joys of life. My personal experiences with keyboard enthusiasts have shown most of the community to be nice, quality people.
When does a strong interest become a destructive obsession? Probably when it interferes with the responsibilities of life. Are you doing well in school? How are you at managing money? Are you a good friend? Are you fair with others? Have you set realistic life goals and are you working toward achieving them? Life can get very busy at times and any optional interest or activity can become a rival to more important commitments.
About 15 years ago, I got together with my old training partner whom I hadn't seen since 15 years prior to then. We both had dreams of being world class weightlifter and spent countless hours in the gym. While our friends were out having fun, we were torturing our bodies. While they were drinking beer and getting high, we were swallowing supplements and gulping down protein drinks. As we talked and reminisced, I casually joked that we sure were stupid. He disagreed and reminded me that we turned out okay and that many of our friends didn't. The goals we set, while in some ways unnecessary, at least protected us from some of the harmful excesses that destroyed some of our friends lives.
I have gone through many obsessive phases in my 62 years of life. Many of them much stronger than my interest in keyboards. I think that overall I've gained from all of them. With each, it added a, at times useful, piece to the repertoire.
One more thing about the keyboard hobby. There is something pure about it. We don't do it for fame. It won't help your dating life. It offers little hope of prospering financially from it. We just do it because, for some hard to define reason, we enjoy it.