Open plan is just kitchen/dining/living room? We have that now and I love it. Have never seen a toilet in a living room.
Having no walls between kitchen/dining/living works so well for us, this is the first time I have had a house with more open plan & it does look bigger and keeps everyone from crowding me in the kitchen when we have parties.
And walls don't cost much - we moved some around when we bought this house and interior walls that are not structural are affordable (compared to other renovations).