Jack --

thanks.. 1/2' black pipe is about $12 for 10', galv maybe a few
dollars more. I'd think 1/2" pipe 2.75" deep in the wood and
extending 12" out (120" / 8 pieces = 15" per piece) would be very
strong, capable of holding well over what I'm putting on it. I'll
angle them at 5 degrees or so. I don't like the 3" of wasted space
against the wall, but not sure what else to do. I can grind a spade
bit down to make a snug fit for the hole size. I don't want to drill
all the way through as my shop wall is drywall.

Those L-brackets were a cheap and simple idea. But the cost for pipe
and the 2x4s is the same or even less, just a few hours more work.

I have this cart, http://www.scrgeek.com/woodwork/storageSheets.html

which has potential, but I think your cart has better all-around
versatility. I just about built that one, but built mine because I
have about 20 sheets of plywood. But with all that weight, even with
steel wheels, it's not that mobile. I'm going to have to succomb to
the notion that I don't have a good way to store my beloved plywood.

I have even been contemplating a 50" x 98' assembly table with room
below for the plywood, but that's more assembly table than I need,
though I'm thinking to build into the base drawers, storage
compartments, and outlets on all 4 sides for quick power access for
drills, sanders, etc.