I'm aware that room separation lines are associated with levels because rooms follow the same principle. I'm not disputing that it should be that way. I don't know what you are trying to add to the discussion by pointing out the obvious.
Cropping the working views is a work around, but I thought this forum was an place for suggestions for improvements. Regardless of whether there is a work around to show only the separation lines at a specific level via view range adjustments, it would be an improvement for a room separation line to report the level it is associated with in the properties palette so you could save the effort of adjusting view ranges, if you so choose.
A second suggestion would be yes, a height property to the separation line, functionally turning it into a room separation plane. I also realize this would be a more complicated suggestion to implement in the software, but again, it could be a worthwhile improvement. Basically, to replace the current 2D room separator line paradigm with a room separator plane that acts as an infinitely thin wall with top and bottom constraints and no materiality, , dividing up a space as walls do. Again, that is a suggestion for improvement to the software, and not a misunderstanding on my part about how the software currently works.