So is the answer 'No one really knows'
Not copy/pasting stories is not always the solution. There is a ratio. As an experiment on my other site (which I didn't use) I set up a plugin on wordpress to automatically post from a RSS feed. Since installing that plugin about 2 months ago my traffic has went from 200 uniques a month to around 1200 uniques a month. (Not a massive amount of traffic but a increase none-the-less)
I'm just wondering what the ratio of unique/copy is acceptable?