My 2-cents here I would say that working smarter directly related to developing your leadership skills. You can do a lot more by helping lead a group of technical people than you could ever do/code by yourself.
Very true, but if you're in your late 30s, mentoring and leading other developers is mostly likely part of your job description. You are in a position to make broader multiplying impact than a junior developer with only 2-3 year under belt.