We have a perfectly good dishwasher at home in the house. It never gets used. It's actually full of dishes for storage. Why would we want one in the camper?
Yet, some folks think the same thing about washing machines and clothes dryers.... why would anyone want one in their camper? Yet, we do. It's used almost every day.
So, basically, it all boils down to what you want. No two people "do camping" the same way. What giggles one person, nauseates another. So, although we do dishes by hand in the sink, there's nothing wrong about someone else doing dishes in a dish washer if this works best for them.
I have no response on dish water consumption though. Doing dishes by hand in the sink has never put us in a bind or jam with water usage though. But, we (almost) never boon-dock either. We always have access to water and a dump station somewhere.