I think that wordless picture books are often overlooked for older readers. We often use wordless books with young readers because there is no text that they are required to read in order to understand the story. However, I think that there are some fantastic wordless books for older readers that invite the reader to really ponder what the author is trying to say. Because the whole story is told through pictures, there are often subtle hints that the reader must notice in order to fully understand the story.
These books invite rereading and are definitely suited for more mature readers.