There are a lot of bugs rejected, because they are duplicates, but from personal experience I found it sometimes difficult to find those bugs. One of the issues here is that the title of the bug would be significantly different, but the underlying issue is the same. Not always would testers watch the screencasts all the bugs submitted before theirs to be able to make that determination. So my suggestion is if there is a duplicate to be counted as +1( reproduction). I assume many would try to take advantage of that, so maybe there should be a limit to it (possibly the first 2-3 reproductions).