At the very least, deleting your account means they won't be getting any extra information. Also, it's much harder for people to link you in bad photos and events, and you won't show up in searches, etc.

Just because they have some of your information is no reason to let them get anymore. You gave Facebook your personal information? Fine, you fucked up, live and learn - but have the sense to delete your account now and stop giving them more. They're only getting better at collecting and using private data.