Yes, if you increase the concentration of either of the two salt solutions you will see an increase in the electrical potential of the cell. What effectively happens when you increase the concentration of the solution is you increase the available number of cations (+) and anions (-) that are available to participate in the electron transfer. If you increase the number of ions available for participation, the result is a stronger net current produced by the cell. Think about it this way: electricity is like a bunch of little electron "people", all lining up for their turn to ride the escalator up or down. If you increase the "people" that are available, you increase the number of people that ride the escalator. More people equals more voltage.