I don't think it is so very mystifying why Evangelical Christians ally so strongly with Israel. Fundamental Christians believe strongly in the Bible. And the Jews in Israel are an important part of the living fulfillment of the Bible's promises and prophecies.
That's my take on it, anyway.
I agree with everything you wrote and don't think it's necessarily a mystery either, except, frankly, to many Jews. And while there is and has been (sometimes vicious) anti-semitism here in America, it is a pale shadow of the centuries of hate and suspicion that they have endured in Europe.
Britain has also been a relatively safe haven, and the fact that much of our national heritage is Anglo-Saxon probably has something to do with this affinity many of us feel. The subject of anti-semitism in all its forms has been well documented. My point was that what I guess you would call the philo-semitism, of the American Christian commmunity has, I think, not been the subject of much research or writing.