You are correct, the increase in wealth has little or nothing to do, directly, with a "look out for number one" philosophy. However, as it requires many data points to support an argument, my graph was the one data pointed needed to attack your argument that "it is likely to be terrible for Numbers 2 through 100, 1,000, or 1,000,000, and a net negative for the country as a whole."
Examine any reliable data stream you wish, the "me first" attitude has not led to the devastation you imply.
Btw, looking out for number one does not suggest or require the "screw everyone else" corollary. Rather than a stingy, the-hell-with-everyone-else attitude, "me first" is actually the best way to improve the lives of people as a whole.
Do you know what I need to make my life better? I readily admit I have no idea what you need to make your life better. Extend this to the entire population. Who is best qualified to make the decisions that will make the most positive impact on any person than that person themself?
You also mention the "shrinking middle class." That would be a terrible thing...if the lower class was growing. But the middle and lower classes are both shrinking. It is the upper class that is growing. This data is widely available but here is one graph based on census data. Over its entire 50-year range it shows a fairly steady decline of poor and middle incomes and a steady increase of the upper-income bracket. Isn't this exactly what we would want?
Yes, the rich are getting richer. But in a free market system, the rich cannot take what isn't theirs. They can only grow their wealth by making their customers better off. Put a monetary value on "better off" and we see that the rich become richer by making other people richer.
However, there is a segment of "the rich" that operates according to your principles. They operate outside the free market and get their wealth directly from the governments (local, state and federal).
I first noticed this in the early 1990s when I read an article praising California's anti-poverty programs. Contained in the article was the amount of money California spent each year helping the poor. It also contained the count of the number of poor living in California. Some quick math showed that California was spending $15,000 on every poor person in the state. This showed that a poor married couple with two children should have been receiving $60,000 in benefits every year!
Needless to say, they were not.
But all that money was going somewhere.
Concern for the poor is a noble sentiment. But it is also quite a lucrative business.