Will adding another water heater boost the water pressure in the house in addition to giving more hot water?

No and yes. No, you won't get more water pressure. To do that you'll need to find out why the water pressure is low. Perhaps flow restriction, perhaps a poorly adjusted water pressure regulator, perhaps low pressure from the well/city water. But an additional water heater will certainly give you more hot water. It would be like putting in a LARGER water heater. In most cities the water pressure required is about 20 PSI. Small city's do not add pressure pumps to their system but use a gravity supply. That is why most places there is a pressure problem either build their water tanks taller or erect them on a hill.