Hey tomd333, can you confirm that re-doing the ground contacts really is the long term fix? I have the same problem in an '09 with a BOSE non-nav head unit.
I started having this problem with my radio (non-BOSE) a few weeks ago. The LCD randomly dims and then brightens again. No other lights dim..just the LCD screen on the radio. Mine did it mainly when it was humid out. When the weather was more dry, it didn't do it at all.
I fixed it by removing the radio from the dash, and then separating the main part of the radio (the metal box part) from the plastic front faceplate with the LCD screen and buttons. There are 4 screws that hold the plastic faceplate to the actual radio itself. When you remove the plastic faceplate, you'll notice 2 metal contact pads on the faceplate circuitboard that apply pressure and touch the metal chassis of the radio. I think this is the ground for the faceplate circuitboard, which includes the LCD. I noticed some dark carbon buildup where the metal pads contact the radio chassis. I scraped off the carbon with a knife and roughed up the metal for better contact, and bent the metal pads a bit so they would apply more contact pressure, and then reassembled everything.
So far, it has not dimmed once over the past week, and the LCD digits even seem to form a little faster. When I did this procedure I also cleaned my battery terminals, but I don't think the battery terminals caused the problem. I could have just brought this in to the dealer, but this fix took 1 hr and I thought I'd give it a shot. I don't know if this will work for everyone but it seems to have fixed the issue in my case.