Is it possible that Mann only added those confessions after a bit of adlibbing? No, I'm not suggesting Pacino and DeNiro adlibbed all the dream talk. Maybe a just a bit of it, but because the talk is so detailed, it no doubt had to be written out. "Cut. That was great, guys. Let me flesh that out a bit." As to the meaning, I'm not sure. We'd have to ask Mann. Dreams can have "hidden" meanings or a subtext (so say some people), so it is interesting that both men want to make themselves slightly more vulnerable to each other.