I don’t approve of being polite (for myself, of course). Not that I have any problem with politeness and civility; it’s just that I don’t think people deserve that much of respect. Experience taught me if people notice you’re a good person, and you respect them, they WILL use you. I’m not exaggerating, and I’m not being pessimistic. That’s how people operate. However, I reckon a little pretend politeness wouldn’t go amiss. Be nice as long as you have a use for it.
And about civility in general; It depends on the situation. Sometimes talking formally to a friend who considers you as his close pal is very rude. Sometimes speaking to someone in an informal way is the best way to be polite. So in this case, the result you get from being nice hangs in balance. It can fall either way. Just be smart. Don’t act too courteous towards a friend; it might be very rude and a relationship killer.