Currently, I have one graphics card doing mining.
If I add a second graphics card, is there much of an electricity savings?
unfortunately for you, at this day n age it is impossible to earn profits with gpu mining you would want to buy a bitcoin miner even the ntakes around 6 months break even unless u get it really cheap price.! good luck tho
If u add second card u will see just double profit of ur single card . Electricity will be higher comsumption!