jwbernin:
I'm not using V+ and GND because I want to be able to invert the voltage to reduce the wear on the electrodes - my sensors are simple galvanized nails, not anything fancy.Yes, I am planning on using a Mega - I've also got 15 solenoids and 15 relays to control (for water and lighting respectively), so an Uno just doesn't have the pins.
In that case yes, you can drive many such voltage divider/sensor points using a single digital output pin set HIGH. As each divider has a worst case current consumption of .5ma (determined by the 10k resistors) you could safely drive 40 to 60 such points and still be well under the absolute maximum current capacity of 40ma.
Lefty