I can't deny the fact that multiple interests can feed other passions. I don't know how many times I felt like I have had a leg up in auditions when I see the question "Can you play guitar?" on the pre-screen form. Also, being a DJ has allowed me to raise money for theatre groups by hosting the events myself and getting rid of the entertainment overhead.
The problem specifically is that you can only spread yourself so thin. I feel like I am good at a lot of things, but I aspire to be great at something. Some people would take it the way it is right now and be, as my mother calls me, a Renaissance Man. Unfortunately it is hard to be a professional Jack of all trades. If I combined all the time I have spent writing articles and playing music into working on my acting craft, I have no doubt that my skills would be far more advanced than they are now. The down side to this though would be that I would most likely not be cast in the musical projects I have done or write my own shows.
So yes, other interests can feed each other, but you just have to be willing to realize that the time spent on one takes away from the other, and vice versa. Maybe pushing one to the background isn't a horrible thing to do when pursuing your main objective, just make sure to keep it in your back pocket when it may help as well.