I completely agree. I was raised to say "please" and "thank you", not because it's makes me look good, but because it's showing appreciation, gratitude and empathy for the other person's work on your behalf. Politeness is about empathy, not self-aggrandizing.

I've been told more than once that just being polite to a cashier or a waiter has turned bad days they were having around. Treating other people decently is its own reward.