Sorry for making a discussion post - I use a non-steam copy of the game so I can't comment. As the title says, wallhung paintings don't add to the beauty or impressiveness of the room - installing and uninstalling them on the walls don't change the stats for the room at all.

I am using walls added by mods (Vanilla furniture extended) so this could be why. I will test with vanilla walls and see if the same happens...