Doug - can't honestly think of any change I would make to the original design. Nothing strikes me.
It just plods away when needed (not all that often in my case, as I don't do a great deal of spraying) and I scarcely give its design a thought. This suggests that I intuitively find it fit-for purpose.
My tests are, first, whether spray odours hang in the room after use and, secondly, whether or not I can see any signs of overspray on the adjacent wall of my workroom. Neither occurs - nor has SWMBO commented adversely (which is probably the truest test)!