Class is definitely one factor but it's too reductive to say it's the only thing at play. I wouldn't even put it in the top five. The main reasons Americans are so Philo-semitic is the power of Jews to marginalise and harm voices on the right who have been critical of Jews or Israel and also the strong presence of various forms of dual covenant protestantism in America. Im sure many right wing Americans do think, as you said, that Jews are just super duper and rich and powerful so that's why they like them but the vast majority have just never encountered serious work critical of Jews and/or have a religion that literally tells them to worship Jews.

Also you'd think if your class/social Darwinism theory were really a major factor then they'd actually have a lot of affection for American Muslims who punch well above the average in America in terms of income. Now I'd be willing to bet first that many of them don't know that but also that even if they did it still wouldn't change their mind. Just as I'd be willing to bet that if people on the American right knew what I do about the behaviour of Jews in America and especially their role in pushing the things they reject then they'd become strong anti-semites no matter how much money Jews have or what they score on IQ tests.