Thanks Ray for the insight and totally get where your priorities needs to be.
I managed to cobble something together over the weekend using a spare h-bridge chip (L293D) and some unholy hacking on the various code examples out there. To be honest, the hardware was the easy bit compared with getting your head around html and json! Works a treat with my main OSPi controller now sending commands to the indoor watering system.
I agree that the ethernet shield is a bit overkill and makes the unit tethered so will take a look at moving to RF as next step.