I'll add my own anecdote to this. I think the point about getting a better job is spot on. I was working a job for 2 years that wasn't challenging me at all and got to the point that it was almost rote. It was at those times that I felt the need to get intellectual fulfillment by coding outside of work. I was actually able to notice a very significant inverse correlation between the nature of my day job and how interesting it was to my "skill development" outside of work. If you are spending 40 hours a week on challenging technical problems, you should be getting all the skill development you need.