For full tank shots (FTS) you can just make a duplicate of your photo, then use Photoshop to adjust the exposure of the shaded portion and patch that portion into the original shot - eliminating the shading. It's a lot easier than replacing the brace. If you have a Mac, as I do, you can do this with iPhoto and Pages - easier than Photoshop.
My old 75 gallon had a 12" wide 1/2" thick section of glass in the middle. I can say that Joe is correct in that it collects gunk. That said, I'd still rather keep the center piece clean than have my tank's light split in half by an opaque center brace.
I wonder if that 12" brace was either a repair or someone removed the brace because they didn't like it and put that one on instead. The brace on my 75 gal is only 3" wide. Never saw one 12" wide. But did see mention of making a repair using really wide piece of glass. Did you buy the tank new that way?