Chucks let me point you back to what Takagi has to say "Remember: Although a home with two or three bathrooms may only have one or two occupants currently, the number may increase if the family changes or the house is sold. Size for the house, rather than the number of occupants." So what may work for you and your family might not work for the new family that moves into your house.
I hear ya, I guess I grew up in a time when no one did anything while someone was in the shower. No toilet flushing, no drink of water, no changing the TV channel, no nothing... There were 6 of us and we did it every day.
Dishwasher was turned on at night before we went to bed and clothe were washed all day on Saturday.
Also, I wouldn't spend a nickel increasing the hot water capacity for the new family. If they want more hot water, well, it's now their crib which comes with the pleasure of paying for what ya need... Ya know?
If they want more they can buy more.