Congratulations — that’s a big project! And thanks for the detailed report.
We discussed the differences briefly when the V3 was first announced.
My guess, though, is that you got the biggest bump in improvement just from replacing the old zwave classics switches with new Z wave plus ones. That would give you a lot of improvements throughout the mesh.
As far as your locks, assuming they are fairly new models, security management is just better on the V3 hub.