Immigration has really made America a culturally and intellectually vibrant nation, for the better.
I will say that another strength of ours is the legacy western civilization bequeathed to us. Our civil and political institutions are offspring of English common law and English constitutional law. Our founding political documents are firmly rooted in Western European Enlightenment thought. Out science and technology germinated from the scientific revolution in western Europe. Our values, ethics, our law, our economics, our system of logic and reasoning, our pragmatism comes straight from the Greeks, the Romans, the French philosophes, Jesus, Aristotle, Adam Smith, the English and Scottish philosophers.
I don't see any need to change that. Confucius, Lao Tzu, Muhammad, the Buddha are all wonderful perspectives on life, but they really can't be the basis of American civilization.