Most people know that a special report/white paper is a thinly veiled marketing piece, but that doesn't stop them from downloading them. That is because people know that they may learn something that may be of value to them. Teaching sells, remember? And there are many other ways to use them.
Many people would rather die than talk to a sales representative out of the blue, but they will read a white paper. When people start researching a product, they are not prepared to talk to a salesperson. They have no idea if the product is for them, or if they will even need it. Well-written, benefit-laden reports will qualify your product or service to the reader. When your salesperson does call, the reader will be more receptive because a relationship has already been established.
Prospective customers and search engines aren't the only people interested in white papers. You should also be using them to reach journalists. This is why you should always include a solid technical section in a white paper detailing your sources and reasoning. Journalists don't want to download a white paper and find a brochure. But a well written, valuable piece of information could get you a valuable mention.
Many corporations go to great expense creating expensive press kits to give to journalists for business opening, product releases, etc. Talk to an editor and they will tell you that they throw away the fancy press kits and keep the white papers/special reports that can help them write an article in the future. There is also a good chance that the company that provided that report gets mentioned in the article.