You'd need to show that CL copied ads from newspapers in order to attract traffic, and I don't believe that's the case. taking away market share and scraping someone's website for content are vastly different things.
I have always wondered about running a similar listing somewhere else first, then running something lightly edited on Craigslist, sending their registered agent, by registered mail, a note that the exclusive license applies only to the relatively minor editorial changes applied.... I wonder how fast such would get delisted....
re: scraping. This is something that has come before the courts a few times (I'm thinking Ebay and a few others; although it might have been called "crawling"). Do you think CL can win on a claim of "scraping"?