Again, pictures would help.... are there chunks of carbon falling off the sides? A plastic scraper from the hdware store would be the thing for that. My 55 probably looks a lot like yours, and I give it a good clean once a year (if I think of it).
If you want to clean the racks and the side racks, get some Greased Lightning or Pro Force (from Sam's), fill a large tub with a mixture of water and the de-greaser and let them soak for a day. I used to do that all the time but haven't done it in a couple of years. The horizontal racks can go in the dishwasher and after its done, they will clean up almost new with a scrubby pad.
I would scrape and wipe, but don't use any oven cleaner or such on the insides.