One of the main reasons I have always found reading Wilson's books is time well spend is that he constantly manages to lead you in one direction, and then pulls the rug from under your feet. He leads one to question some of the most basic beliefs one holds for their validity and almost always provides for a great mental rollercoaster ride.
Another aspect is that his books for me always provide interesting bits and pieces, hints of other works that lead one to explore the mentioned crackpots, authors, scientists and occultists in more detail that a person with a normal western-style reality tunnel might do, if at all. So his having enjoyed a wide variety of education and experiences can really pay off for the reader as well, in an intellectual sense. Without Wilson, doubt I would delved into James Joyce, Buckminster Fuller, Crowley, Timothy Leary and other great writers of this and past times.
The only drawback to his works is that they are so firmly rooted in American pop-culture, that people from other backgrounds have trouble understanding half of what he is hinting at, or are simply not as interesting as they are to Americans (such as the Kennedy Assassination and other Americana often found in his works. I myself never found this to be a problem, but I know of people who do.