It's a logical question. As for a "correct" answer, well, as you can see and read, there is no correct answer. Everyone has their reasons why they do or, don't use camp ground showers/rest room facilities if, they've got a nice motor home they're traveling in. And, it doesn't have to be a class A, it can be any version of a motor home or, travel trailer that's self contained.
We have a very nice motor home. It's an '04 Itasca Horizon 36GD with the C-7 330 CAT and, I've used the C/G facilities all over the place. I don't ALWAYS use them, it's my pick or choice at the time. I don't, never have, and never will take "LONG" showers so, that's not one of my reasons for using them. My showers are "navy" type showers. ON, wet, soap, rinse, done. But, as one poster stated, there's usually much more room in a facility shower than the one in the coach. And, based on time frames, the wife will use the one in the coach and I head for the one in the campground.
Yep, there are some that I walk into and, turn around and walk right out of because they're just to darn dingy to even think about showering in. Others, well, let's just say I've been in peoples house restrooms that are not nearly as nice as some of the campground/RV park ones I've visited.
So, again, it's just a matter of opinion. Use them or, not. Good luck.
Scott