What is the next step after you have excelled in one? Maybe there isn't , maybe you need to keep doing what you are good at. Maybe that is the only way you can retain your edge. Look at Sachin Tendulkar, he has been playing cricket for the last 23 years (actually more, 23 years he has been playing for the country). People who seek change and have the need to "evolve" don't enjoy the same level of success in their "evolved" role.
Satyajit Ray died a great film maker because that is what he did all his life while Yash Chopra has delivered quite a few flops after he decided to just produce instead of directing movies.