dude, google, or call your local police department, for a list of top 10 or so stolen cars, that is the only way to know for sure, the chances. geographically your odds differ....

As vulnerable as you make it. Lock your doors and dont leave valuable crap out in plain sight.

If the locks and ignition are worn you might be able to get in with a bump key, but this vulnerability is present on most cars without chipped keys. As Alex said, keep it inconspicuous, lock the doors, and don't leave a key in the ignition (This is big, because glass is much faster to break that an ignition), and you'll have a lower chance of having problems.

if you are super paranoid, run an extra wire from the fuse with the fuel pump, to a toggle switch anywhere you wish, they cant steal it, if they cant start it...

Kill switch, ftw.

From what the police detective who is investigating the theft of our Saturn SL2, one of the easiest.....