I agree that extends and includes are messy and hard to explain. A friend who wrote a book on UCs once told me that "extends and includes are best discussed by friends over beer." I don't use them. I also find use case diagrams to be of very limited value. Nor do I like Cockburn's use of "extension points" and lumping alternative flows with exceptions.

However, I don't agree that use cases are unstructured. Writing a textual description of a UC in a good template (I have one you can download at softwarereqs.com) and supplementing that with an activity diagram, process flow (flowchart), or sequence diagram makes use cases well-structured and easy to understand and work from.