Where do you find the expired content? and how do you make sure they are actually never been used elsewhere? do you use copyscape or similar apps?
I have been writing articles myself for my sites and it is a pain, I did buy from here and it was trash (even trash is actually better) I could not even fix it, so I decided to just do it myself.
If you can find expired content that is really good and IMO I would just change it a bit here and there and run it through copyscape. But I'm no expert in this field, but I talk from the fact that if I'm google and I have all of these technologies, I would prefer your site to be unique and exciting.