Well, I am unfamiliar with nails, but as for the other two questions, turning off stuff should preserve some power, but the generators can last a good few days. Though, it couldn't hurt to buy more stability when you can. For the signals, upgrading them does reward you more, and allows you to hear the signals as they are supposed to be. Less static and actual sound. Upgrading them all the way to level 3 will net you the most profit and the intended experience of the signals.