Do what you do best is great advice but there is nothing wrong with learning new skills and venturing out of our own comfort zones. I do not know of any great lyricist who does not know the rudiments of music composition. I do not know of any great producers who do not know their way around a studio mixing desk and recording equipment. I know lots of folk who are willing to learn new crafts to enhance their own speciality as a result of embracing, learning and exploring other areas to improve skill and knowledge. It is both naive and insulting to say otherwise.