DavyJones, The boards I have designed for test equipment always have the "extra" area layed out as ground plane. This is true for both sides of the board. Then the areas are then stitched together to make 1 ground circuit. This allows for the lowest resistance path for the return. If I had to make my own pcb's this is what I would do also as to save the amount of etching of the copper and prolong the usefullness of the acid...

Dave Purola,
N8NTA