I don't believe his general values should be taught as such. I think his farewell address is a pretty important part of history that I'd venture a guess few have ever read.Washington's farewell address is not the law of the land and his thoughts on general value of religion are not that important. Why should it be taught?
Saying that the good of the country can not be seperated from a religious belief is pretty much encouraging religion. You are perfectly free to disagree just as being a citizen also he had a right to note.Besides, that as I pointed out, it is not at all the same. Washington was giving his general opinion on the value of religion as it concerned civics. He was not using the power of his office to encourage a specific practice of religion, in this example.