Thanks everybody who responded. In summary what I got back from you all (and with some of my own research):
C-Bus is robust and reliable but expensive, there are existing installations with openHAB, but not many, and there is little activity on forums.
Z-wave is good solution for controlling hardwired and plugged in devices.
- It is not “cheap”, but a wired in-wall light controller is ~$80AUD locally, and cheaper imported.
- Products can be imported but must use Australian/NZ/Brazil frequency 921.4 MHz
- There is lots of activity/support in the community
- There is an open issue on the Raspberry PI with openHAB related to duplicate messages, but otherwise it seems to be reliable and working well.
- Z-wave locks are not yet supported (security classes not implemented in binding)
- Can be used for sensors, but if you have lots of sensors, there are much cheaper options.
Some other alternatives is to control lights using wired relays (certainly possible but I like house wiring to be fairly standard), other protocols like Zigbee didn’t get a mention…
So now I think I am in the same boat as a few of the responders, and try to source cheaper z-wave products.