I have a Rev C-5 with 65 devices. Some virtual. Healthy mix of Lutron, Z-Wave and Zigbee. I have no complaints about my current setup.
Is there any compelling reason to upgrade the hub? How much work would it entail? I have no interest in rejoining dozens of devices. I see there's a migration option available, but it's unclear to me how turnkey or comprehensive it is.
The only thing radically different between the C5 and the C7 is the z-wave radio. (IMHO). C5 uses 500 series and C7 the 700 series radio.
So unless you see the need for an upgraded z-wave radio or another hub to split/load share devices/rules etc, personally I wouldn't bother.
Having said that I have a C3, C5 and a C7. and share my rules and devices across them.
My C-4 is used for cloud stuff like Amazon Echo etc. My C-5 is for Zigbee since it is my understanding that the ZB radio is the same as what is in the C-7. The C-7 is for Z-Wave to take advantage of the new chipset. Use HubMesh to communicate between the hubs when needed.
I also agree that it is not necessary to upgrade either, C-5 should be fine. If you ever do decide to upgrade though the migration service should make it very painless.
If you got Fibaro, then dont do it, It will pair using s0 but my network seems fine. 10 S0, 13 none. Slightly better debugging for z-wave. Running 2 hubs now zigbee & zwaves one.
Power metering works fine for me.
Unless you need a series 7 network, then no, it's not worth the hassle in my opinion.