You have about the same chance of something happening to your car in Columbus as you have of someone breaking into your car and taking your coat (which had your house keys in it) and your IPad in Ann Arbor - which is very slim. Unfortunately, this stuff happens every where. I know what happened to me in Ann Arbor was an isolated incident and is in no way representative of the city as a whole. I know it is fun to say how horrible the 614 is and how we are all degenerates but I have lived in Columbus my entire life and it is one of the nicest, friendliest cities in the Midwest. Don't look for trouble and you won't find any.
Also - the Convention Center is in a nice, up and coming area and is within walking distance to tons of bars and good restaurants. I would check out this out before going - http://www.shortnorth.org/dining