If tanks with dividers worked well, I would think more LFS would use them.
You would have to use something besides plexiglass I think, probably more like a mesh. If not that, then you would need to drill lots of holes on the plexiglass just to let the water flow through. Otherwise you're going to get huge resistance from the water pressure, plus circulation won't be very good.
Unless the tank were very very deep, only two lengthwise dividers would fit, I think. Even a deep tank like a 75 gallon is only going to give you about 11 inches each, if divided once.
I would think it would be much easier to get a dual 75 gallon stand and use two vertical dividers on each one. If this is a retail system we are talking about, 2' of space is plenty for a short time. Putting two 75 gallon tanks on a dual stand might make the clearance very tight for the tank on the bottom, but a DIY stand built with this in mind specifically would remedy that.