Sadly if you have a convertible they recommend that you leave your car unlocked otherwise someone might slit your top to get into it and that is more expensive than whatever is probably inside it (as well as they will get it either way.)
I had a Jeep Wrangler softtop with soft side windows. They cut the window on the passenger's side, which I didn't notice until the next morning. Stole small change out of the ashtray, some CDs, most of which were worthless ones burned by me, and a small toolbox with a, $18 multimeter and some electrical terminals and tape. Nothing taken was worth the $75 it cost me to replace the upper door piece, and I got off easy only being out that, but it just goes to show you that they'll steal anything, whether or not they can turn it around into cash.