I've made a couple trips in the upstairs of a 747 this year. I can tell you that they definitely are not larger. It seems like they put some stuff in there to make the trip more pleasant (ie flowers, hand moisturizer) which they might also have in coach.

During these trips, I like to change clothes twice (ie something to sleep in after dinner, something to wear after we land). There definitely isn't any extra space for that.

For United: It seems one big bathroom would be better than two small ones.