Maybe I shouldn't be so negative about it since I haven't worked with hidden elements in Revit so I don't know all the positives and negatives. But if you really need to "hide" elements and don't like the idea of having one or two extra layers for some reason, there is a way of doing it in Archicad even today.
You can create your own Renovation Filter, for example called "Show with Hidden Elements", select the elements you want to "hide", click on the button "Show on current Current Renovation Filter only" in the Renovation Palette and then it's going to be hidden on every other Renovation Filter.
I know the Renovation Filters were not meant to be used for that, but it would do the same as an extra "Hide" function.
But I still think it's much easier and more natural for the "standard" workflow just to create an extra layer. "Hiding" elements creates a potential source of troubles later in the project or when someone else takes over your work. Also, it doesn't sound like it would have to be too many new layers for the first example you gave. And as for the second example, I'm not sure if I quite understand your problem.