Matt, I like your ideas. Were it inadvertant plagiarism, I might do something like that. I agree about the levels of plagiarism and I've seen them all. Blatant is what I fail people for; inadvertant is where an in-class punishment (and not an easy one) is more advisable. At the same time, though, prevention is key, and I hope I adequately warn my students about it.
Solitair, you make a great point. I hate regurgitation and hopefully my students are learning not to. On our final assignment I purposely discussed the text very little and the concepts very broadly so they could assign their own value to the literature. And as they go on through college, ideally this analysis will become more automatic; I don't think freshmen, whom I teach, should have to analyze as thoroughly as seniors, but they'd better start learning how to do so. That tool is probably one of the most important things students learn in college. Good point.