Great thread! I feel the same way with many things at my work, both built by me long time ago or the staff before me
Not easy coming with ideas when I haven't seen the tank and all the angles first hand. But I can try!
Just like you wrote, magnets for streamers in the dry box. Maybe also in the overflow box, if the magnets are okey with being in water. No easy task to take out them and clean though..
Maybe try a more light rock work, accepting some of the black wall become visible. With some rocks and corals in front of it I don't think anyone will notice the black wall that much. We've done a couple of pillars with drilled live rock and an acrylic rods or a PVC pipe inside, allowing us to stack rocks of different size on top of each other. This way the base doesn't need to be so wide. You could also run the pipe/rod all the way up and attach above the surface if you want it to be more secure. I can post a couple of pics of our pillars when the light come on later.
If you want to hide the gyre pumps you might try them behind the rock work on the back wall, outlet pointing upwards the surface. But then you need the tank to be water safe above the surface where the water comes up. This can create a pretty nice wave from the back top of the tank.
We have a couple of 1 meter deep tank and I really hate them.. I can't say I'm happy with them even if I've had many years to work with the rock design. I think I've gotten to the the stage "good enough" and then just let them go.
Keep up the good work and keep the posts coming! Some more pics of the tank would be great.