I completely agree with you. If I ever teach a creative writing course one of the things I would strongly encourage my students to do is explore an interest that has nothing to do with creative writing (unless they are interested in aesthetic theory, since that can get fun, philosophical, abstract, etc). Granted, it's easier to explore second interests when we are no longer students and we are writing full time. What's one of your non-writing interests? I have three I think: life improvement, dogs and sex! The dog interest is interesting right now because I want to rescue a second dog but our dog Yago isn't very nice to other dogs and still needs more training, I fear.