I have to disagree. The Heather Poly Gibson Bass IV that I had had severe discoloring on the headstock from where it had been hanging on a hanger that reacted with the nitro finish, and my Rickenbacker came with two spots of finish missing in the same place where a previous owner was not careful about hanging it by the neck.
I have a SG guitar and Thunderbird bass that I have owned for over 40 years; they have both lived in their cases the whole time. Nothing bad happened while in their cases and finish checking is minimal on both. I still think in the case, under the bed is the best place to store a bass.
However Pilgrim, I like your wall hanging scheme, but I would hang the lower row a bit higher so that the bottom row headstocks were midway up the necks of the top row, alowing more room for movement.
You're right that hangers can discolor old nitro finish necks - if I had been thorough I would have pointed that out. However, with finishes other than nitro it's no problem.
I think your idea about moving the bottom row UP is excellent! That hadn't occurred to me! Moving the headstocks up so they weren't opposite the widest part of the upper bass bodies would be very helpful.
And if the bottom row moved up, the top row could move down a scosche....since the vertical spacing would be more compact. However, the top row has never been a problem.
