Ataris are easy to get looking new as long as they're not truly beat up. You can just take out the insides and drop both halves of the shell in the sink like a load of dishes. After some quality time in the warm soapy water and some TLC from a toothbrush, those puppies will look like you just pulled them from the box. A little packing tape and card stock over the serial number will save that gem as well. For anything else that's not so sink friendly, Windex has always been my savior.
For just one example (and man, do I wish I had taken before and after pictures as you had) my manager gave me a couple of Atari 2600s that were just dirty as hell. One of them was a Vader but I didn't find that out until after I washed all the dirt off the thing - I'm not kidding. Now they both sit proudly and seriously get complimented on being the nicest Ataris some people have ever seen.