IF sponsorship didnt increase interest and sales they wouldnt be spending millions or billions on it, esp in this economy. Facts are just because you or some others buy something none related to sponsors, you cant assume that the majority dont pay attention to commercials and sponsorship on nascar or anywhere else--it works--or they would NOT be wasting the $$$'s, but those its not working for they usually drop sponsorship.
There was an article about the Nationwide Insurance commercials that Danica is in and Dale JR shows her phone number and they reported that they get over 50,000 calls to that number and of course its an advertising gimmick directly to sell insurance. They report great increases in Hits on their site also --because of the commercials, so dont be suggesting that commercials dont work because they work for Nationwide Insurance and they have worked to help Godaddy grow as mentioned, and most others otherwise they wouldnt be wasting millions of dollars on them for sure--look what big co.s pay just for Super Bowl comercials--now thats crazy--but it must pay off? However--Yes--there are some very rich people who do sponsor products, cars etc just because they are rich, or need a tax write-off, but that is not the norm.
However--I will say that i dont often buy products simply because of commercials/sponsors etc--but-- I have saw commercials that made me interested enough to check out the product, so its working getting my attention, whether I buy the product or not--its a big part of business?