Мы с тобой друзья. We are friends. Or does the Russian emphasize the individuals involved?
Мы с тобой друзья. = You and I (just the two of us) are friends. Moreover, the sentence is unambiguously addressed to you, my friend. (E.g., English "The two of us are friends", while conveying the same information, could be a description addressed to some third party.)
Мы друзья. = We are friends. This could describe an arbitrary group of friends, and the sentence can be addressed to anyone.