You can tell a blog is past its prime when every post is unsettlingly familiar. Sometimes it’s the niche. Maybe they went too narrow, or maybe the niche sputtered out. Maybe the blog is so old that the writer doesn’t know he’s on the 20th variation of the same nugget of wisdom. You’ll see it on most internet marketing blogs in the form of the bi-monthly “Use membership sites to make money” post. It’s always the same, even if the words are different.
And some things are just plain tapped out. You might squeeze more life out of an old subject, but it’s rarely worth the time. It’s why I couldn’t make the blogging blog thing work. All the ideas I had were repeating themselves or contrived to the point of uselessness.