This will be an issue when someone launches a site like interesting-cars-on-google-maps .com.. (not a real address)..
At the moment, everyone is in the same boat with valuables etc. However, for the classic / special / modified car owners, you would need someone to purposely FIND your car on it to steal it or whatever.
SO, at the moment, like HRC says, its only like knowing that a classic / yank / whatever is at a particular address as you are a local or something.
Issue comes if someone collates all the information together with links, then someone can just go through, pick what car they want, find it on the maps and go get it...