I need to address:
-the lower vanity
-the upper vanity
Re the bench, with a half wall, there would be no gap, as the bench can butt up right to the half wall.
Re the lower vanity, again, with a half wall, there would be no gap, as the vanity can butt up right to the half wall.
Re the upper vanity - potential aesthetic problem (no Swiffter problem), as there would be a gap between the side vanity and the glass, and even without a gap, the entire side vanity is visible. So I think only the full wall addresses that one. Hmmm. But what might work there is what is shown below where the sill of the half wall continues up the wall. This address the 'gap", but of coruse ones still sees the side of the vanity while showering. Maybe its not so bad - dunno.