While this seems like reasonable advice, I'm not sure it's universally good advice. Richard Feynman seemed to enjoy a level of charm many of us couldn't hope to possess. He also had a wide selection of esoteric interests unrelated to his field.

I would also claim that there's value in simply maintaining such an interest. During particularly insular periods where I'm absorbed in less accessible work, I find myself starting to exhibit "aspie" characteristics, losing verbal fluency and becoming socially insensitive. It's not just about having things to talk about, but maintaining my own faculties for relating to people.