While I would be tempted to take a fabulous bag, I wouldn't. Thieves are always quite honest that they target people with designer/high-end items, and sometimes a theft can happen so quickly it will seem like it was all a blur. Someone on the Rick Steves grafitti board said that someone ripped them off just as they stopped the car, and that if it hadn't been for the seatbelt with one passenger, more would have been taken than some bags in the back. It's also pretty routine for rental cars to be broken into.
What I would do instead is buy a nice bag toward the end of the trip and then use it on the way home if was practical to do so or just keep it in the carry on.