I haven't seen Keita or Nzonzi, but Matuidi is a quialiy player and in many times he can be more useful than Vidal. He is also much cheaper.
And I prefer to discus real transfers instead of rumors, most of which are made up anyway. So far Inter have been linked with the best players in the world and they haven't signed anybody. Just like they were linked with Simeone, Conte and Pocchetino and ended up with Spaletti.