I don't think collapsing comments is the perfect solution, but is better than nothing. I don't have an answer, I don't believe anyone has it ready. If anyone knew how to fix the way we talk to people over the internet, that person would be rich by now.
I agree. I'm often struck by how threads on HN, Reddit and Google+ about some topic go together and pick up on where past threads left off, or duplicate them unnecessarily. (brings to mind that David Byrne line "Say it once, why say it again?")
