You don't give enough information on you topology to give proper guidance. I'm assuming the 9ks are the vPC root and your spanning VLANs to the down stream switches. Your topology sound super simplistic.
ACI is the ultimate DC network solution (Did an NSX demo and did not like it). Super fast links (100Gb), inherently HA topology, crazy options for traffic engineering, host routes injection so no need for OTV+LISP and a bunch of other options. In my opinion, if you don't need some level of segmentation that is dynamic and the options I stated above, you are probably better off with whatever solution you have now. I only say this because ACI has a big learning curve and you will have to learn how to do thing differently. Its not like deciding to upgrade from Catalyst switch xxxx to zzzz cause they are faster.
