I agree on the Polish.

Thats an old trick for selling a used car. Getting the glass to sparkle, can add that "hmm this ones not so bad" touch, to an older otherwise dismal looking car.

A dealership I did some detailing for, a long time ago, used 0000 Steel wool soaked in glass cleaner, and it worked excelent for any stubborn build up. Like a smokers car.

I also had this glass cleaner from Castle one time that went on like a wax.. worked very well.