I was at Springfield Saturday and Sunday and never heard any public announcement about a car being stolen, or anything missing. That is not to say it did not happen, only that I was not aware if it did. There was an announcement via PA Sunday mid-day that a rodder was looking for an open trailer to get his car back home to KC due to a mechanical problem, but that's all I ever heard.
I will say that there were several nice cars sitting unattended with keys in the ignition, which I found surprising. Sure, the chances are good that no one is going to bother things, but why tempt fate?? Bruce Lee's suggestion on the brake is a good one, and LoJack tracking is another. If they get it you at least have a chance of it being tracked via strong GPS.