The last time I contemplated extra credit, it was because I wanted stuff. I still can't do it. I can't shake the feeling of grades for sale. But now, now I'm doing it as a carrot for increased team work. Getting my kids to talk to each other in meaningful ways have aways been a challenge, and giving out team points always struck me as a little unfair because I want my students to be in control of their now destiny (and I don't want to hear any guff from my students' parents about that either). This year, I've ameliorated that by including the team tests with all other quick assessments. But that isn't increasing the level of team work. My current idea: allow extra credit, but only in the group/team work/participation category.
Stuff to ponder.