I have a Micro/Wizzy10 setup and also some experience working with an AI Ten2 combo.
An additional speaker will make a difference in volume, but speaker cab efficiency will affect how much louder.
The Ten2 EX (a relatively low efficiency cab) would add a little more volume and certainly more depth. Another Wizzy 10 (a high efficiency cab) would add more volume and a little more depth.
Cost might also be a factor with the Wizzy 10 selling for less than the Ten2...and there are Wizzy 10 cabs on the used market regularly, since they seem to be an acquired taste that some players don't bond with.