This approach tends to work better for articles that are jam packed with information and/or those that take a broad, aerial view of the topic, but it can also work with articles that are a close up view of one specific topic. For example, I've written many articles on how to create an effective resource box, and from that one very laser beamed topic I have branched off articles on extremely specific elements of that already specific topic. I assure you, no matter what your article is about, you can write about it more in depth in a new article.
Alternative Homework for Blog Owners: Look at your recent blog posts__are there any insightful comments that are worthy of being addressed more in depth in an article? I get ideas all the time from comments on my blog. Or look at your blog comment replies__do you find yourself writing an in depth reply to anyone's question about your post? That is often a good indication of a related topic that could use some more detailed attention.