@dlowan,
I'll be interested in statistics on that at some point. I figure a lot of people who already know Mexico wouldn't suddenly not got there, although some would choose another destination. And some newbies might well be scared away. On the other hand, a lot of US vacationers may want to travel closer to home for a while, due to the economy.
On the business about the police stopping cars for trumped up charges about driving violations, that happened on my visit to Mexico City in '69? 71? My friend, a dental student, pulled out the equivalent of ten dollars (if I remember right) tucking it in with his licence to show the cop. Nothing new.