conditionals - If I Were You and You Were I

These are song lyrics, so there's poetic license--yes. However, it raises a grammar question that some friends and I have wondered about for years.

Song goes:

If for a moment I were you, and you were me, how would it be?
Would you fall apart as I walk by?
Hang around to catch my eye?
Be jealous of another guy?
If I were you and you were I?

It's the last line: is it wrong? If one can say, "If I were you," why can't he flip that around and write, "If you were I?" Does it have to be "If you were me?" Or is that even correct? "If me were you" certainly isn't right. So why is it correct (if it is correct) to say, "If you were me?"