The "coming apart" of American culture isn't because too few people watch NASCAR or eat at Applebee's, it's a problem because in one America lots of people do it and in the other America people never do it. It's slowly creating two separate cultures where people have trouble relating to each other because they're growing up with two distinct sets of cultural experiences. It's only incidental that the divide in culture is being driven by meritocracy picking the haves and have-nots.
I'm not surprised you found the results unimpressive, since Britain has a far different history with class and mobility than the United States. I was impressed with how the questions ascertained that I'd grown up in a rural area then moved to a wealthy suburb in adolescence. Things like going to parades, eating at Applebee's, or going fishing were strongly present in the first half of my life and completely absent in the second half. I crossed a major divide in American culture without even realizing it.
I'd argue that there has always been this divide, or similar divides through the course of US history. There's a rural/urban divide which has slowly but inevitably moved in the direction of the urban side throughout the last 100 years. There's a rich/poor divide which I already referenced as haves and nots. There's an educated/uneducated divide which closely mirrors the wealth divide.
None of this is anything new.
You seem to have some beliefs about US history which I don't share. I don't believe in the myth of upward mobility in the US, while there are certainly examples of this, the story is oversold. I don't believe the society is as meritocratic as it is made out to be. The biggest predictor of a person's success is their parent's wealth.
I'd also argue the fact that you apparently crossed this major divide in American culture without even realizing it suggests that maybe you didn't cross a major divide of anything at all.
This is without even going into the immigrant/religious/racial divides that exist. We aren't going to have a homogenous group of 300m people - this isn't a bad thing, and it isn't a new thing.
I'm not overly impressed.
I scored 27 but I'm a Brit living in the states and a lot of the blue-collar culture stuff doesn't translate (NASCAR).
I'm perfectly fine not being involved with the more pop culture stuff. I've only watched House of the shows they listed.
Is this a worrying new trend though? I'm pretty sure the world has always had its haves and have-nots.