I dont think it is recommended to polish a brand new car because it will have, or should have been waxed by the dealers valet prior to you getting it and also I was told by the valet in a garage a while ago, that once a car has had a good waxing, it only needs to be washed with water for a few times otherwise loads of shampoo washes away the wax, much like when we wash our hair with shampoo, it washes away the natural oil in our hair. Could be the reason that some cars need waxing more often than others, because some people put so much shampoo in their bucket, that it cleans of the wax and the shine. I think car washes, automatic or diy are the worst methods of car cleaning, because they apparently use really strong chemicals in their shampoo which is dispensed automatically, probably a bit like dish washer liquid, which strips off everything!