Janelle,
Our classes are about student learning. Students are interested in extra credit because they want (or need) additional points to achieve a certain (or passing) grade. So, we are interested in learning and extra credit is about points and grades, which are really not the same thing. I feel each instructor has to decide how (and if) they want to include extra credit. Personally, I do not, I state it in my syllabus, and students know not to ask.
Barry Westling