I haven’t read the story, and I don’t disagree with your main point, but I think these points are a bit too rosy to be real. One of George’s biggest characteristics is that he feels Responsible. If the audit happened and the savings and loan was short, there was a real possibility that it could be closed by the government or put up for a forced sale, which no doubt Potter would buy so he could own all those mortgages, and that George would be ruined and possibly go to prison. (I take the film’s word for this point, it seems plausible, but I’m no expert.) And his entire life had been a struggle, look at that rickety old house they lived in. They had enough, barely, but “things had been so good” seems like a gross exaggeration.
My favorite part of this film is the relationship between George and Mary, and the way it builds into something like what you hope your parents had, and that you might have one day. It’s aspirational but still very real. So yes, I like the film, although I have no urge to watch it any more, I’ve seen it so many times.
I don’t think the message is buried at all. The world needs responsible and loving people in it, without them it goes to (almost literal) hell. It isn’t necessary to screw every possible last cent out of people and to drive them to disaster doing it, while enjoying the power to do so; you can just make a decent profit and live a good life. George and Potter are archetypes, between whom most of us live our lives. Is it bad if more of us try to be like George instead of like Potter?