I fail to see how Darmian and Witsel would significantly improve us. In the case of Darmian, I don't think he is an upgrade at all.
I guess it all depends on who the draw throws up. If we get Real or Bayern, the management will definitely have to add someone of significant quality in January.
Names like Rincon should definitely be avoided. We don't want to end up with another Stururu or Hernanes, players who will be incredibly difficult to dispose of later on.