My experience naomi is this. I was brought up in a wealthy family, we had a swimming pool, stables, tennis court etc but my parents were (and are) working class scousers who had worked hard for the money. My mother's mother had a motto 'manners maketh man' - so us Lloyds' have always been very polite in povery as well as in wealth. Along life's path, I can't say I noticed any difference between the financially well off or the financially strapped until (and it's a big until) I took my son to his first day of private school. I have never in my life met such a gathering of rude, cliquey and downright mannerless people. (mothers but some fathers as well) It has actually affected me in the past, not knowing if my 'hello' was going to be responded to or whether the person who walked through the door first just didn't realise that anyone was behind them.... I could go on.
Back to the question...In my personal experience good breeding does not belong to the wealthy at all!