Sofa isn't a necessity, but I want some comfy seating inside that doesn't cram you into the dinette. I would forego the couch and associated foldout bed for 2 swivel chairs or recliners. The couches in RV's are always too small for 2 people to be comfortable and unless its a foldout fullsize bed, its too small for an adult to sleep on.
As far as I am concerned, a visiting child can sleep on a sleeping bag on the floor. No need to have an uncomfortable couch for the rare occasion I need an additional (and uncomfortable) bed.