I can’t remember who it was, but I listened to a podcast once with an author talking about how more authors should write books on the same topics.
Instead of trying to tackle new topics with each book, they should focus on making the ideas in their books more concise, persuasive, and powerful.
I think this is true with blogging as well. Most people are afraid to write about things they have already written about. But any time you write about a topic with more experience you will have new insight. Since you have already played with the idea, so you know it better and can communicate it more concisely.
After writing about the topic again, it may turn out that you did a better job of communicating the idea the first time, but you may also find that the second or third time you write about the same big idea, you hit more clearly on the key essence of your point.
When you dismiss topics that you have already covered, you are closing your mind off to lots of original ideas and insights that you could have by simply starting out exploring unoriginal terrain.