Plato's Sophist is interesting because it illustrates the dialectical analyisis and the use of opposites. It's one of the better dialogues that I have read and I am a little disappointed that it was not in the book of Plato's dialogues that I have. As to the Stranger being a god, that is probably hyperbole although I suspect that Zeno played Son of Hermes when he and Parmenides visited Athens and met with Socrates. The Sophist probably draws from the philosophy of the Pythagoreans rather than that of that of the Athenians.
Cicero's De Officiis which discusses ones moral duty in serving society is good reading. Cicero had an inclination for philosophy and studied in Athens. The book is addressed to his son. Marcus Aurelius and others have done similar works. De Officiis was the second book to appear in print. It later served as a primary introduction to Latin. James Madison, who studied at Princeton, probably read him as part of his course of study. Thomas Jefferson had several works by Cicero in his library which were later donated to the Congressional Library. Much of what Cicero says is still relavent today.
Both Plato and Cicero wrote works discussing the republic. Much of Cicero's De Re Publica was concealed as a palimpsest until 1822 so it was not available at the time of the US Constitutional Convention.