Every five years or so, my wife asks me, "What do you need to learn now for the next 10 years of your career?"

If you're self taught, you can teach yourself the next thing.

You don't have a solid CS background? You can teach yourself that. Go look at, say, the list of MIT courses for a CS degree. You don't have to take the MIT classes. But which of the things do you know, at least to some degree? The ones you don't know, do you feel the lack of any of them? Have they held you back at points in your career so far? Go learn those.

Your work isn't interesting any more? Look around at your company. What work there would be more interesting? What do you need to know to be able to do that work? Go learn that. If things line up just right, you can help out on a project in that area that is short-handed, and get experience on your company's dime. You may have to be able to say "I know a bit about that" first, though, so go learn at least a bit about that.