I balance non fiction by reading multiple non-fiction books at once and then prioritizing and making time investment judgements based on current needs. I typically am reading 4-7 non-fiction books, where 1-2 are related to the professional development component of my work, 2-3 are related to the research component of my profession, and 1-2 are for personal interest or personal development. I would assume the ability to do this correlates with how comfortably a person is with multi-tasking, which you seem to be. And, of course, I abandon what is not of inte...
Oh, I didn't mention in the post that my formula is roughly 50% professional related, 50% personal related, and the personal is divided equally into non-fiction and fiction. I also try to divvy my reading time up at the same proportions.