Interesting thread and something I've thought of often. I grew up middle class, but even so my parents lived below their means and we lived in a lower middle class area of town. We did not have a nice house and our cars were always used. However, I was around upper middle class kids all the time as I went to a private Catholic school.
Both of my parents were very smart but had no ambition, so had ok jobs that between the two of them kept us just in the middle class. But education was important to them, as were manners, good grammar, etc. My interests were in tennis (belonged to the club) and skiing, I liked nice clothes, was intelligent and well-manntered, and always was well groomed. Thus, to my friends' parents, I came off as upper enough to fit in.
I had friends who were both middle class and upper middle class. A couple of the upper middle class kids had parents who were millionaires (bigger deal in the 70s and 80s). As I got older, I realized the stark difference in the upper middle class homes to ours, their cars to ours. I always wanted nice things. I had taste, what can I say, but I rarely got them unless I bought them with my own money.
Anyway, we middle class kids noticed as we got older that for many (probably 3/4) of the upper middle class kids, all looked well on the exterior but inside the home it was a mess. Bad marriages, substance abuse, neglect, anorexia, abuse (especially emotional), etc., which all led to a host of emotional problems for the kids. I also learned that some lived the upper middle class life but on borrowed money. I had one friend who at 16 was given a BMW, her family always went on exotic vacations, they had a beautiful home, expensive cars, etc., but I later found out the father just declared bankruptcy every 7 years to wipe out his debt. Unbelievable.
Now I make a great salary (as far as I'm concerned) as an attorney that puts me in the top 10% of earners in this country and have the upper middle class money. Almost all of my colleagues grew up in the upper middle class and most are into material gain and promotion. They earn money to buy more stuff they don't need and keep up with the Joneses. I shocked my firm by taking myself off partner track to become counsel for the firm. No headaches that go along with partnership and I still get to do what I love (yes, I enjoy being a lawyer) and I make a great living compared to my parents. My colleagues can't understand why I did that. They equate more money with more happiness. It's sad to see the same cycle repeating itself with my colleagues that I saw with my friends' parents growing up.
Of course being middle class does not shield you from many of the same problems. I saw plenty of divorces, substance abuse, bad parenting, etc. But I did see what I thought was more of an emphasis on the exterior in the upper middle class and I see it still today.