A couple of points not considered by the Farmdoc article.  First benzene is quite valuable as a precusor for a great many chemical products and as a percentage of crude oil quite small.  The amount of benzene available is essentially limited by the total amount of crude pumped.  It's not like you're going to pump the crude, extract the benzene and then just dispose of the crude.    The current price is a function of it's demand as a synthetic precusor and gasoline additive.  If you started using more of it as an octane booster it's price might rise rapidly.   Quote Wikipedia: "Benzene is a colorless and highly flammable liquid with a sweet smell. It is mainly used as a precursor to heavy chemicals, such as ethylbenzene and cumene, which are produced on a billion kilogram scale. Because it has a high octane number, it is an important component of gasoline, comprising a few percent of its mass. Most non-industrial applications have been limited by benzene's carcinogenicity."  
  The second point is it's carcinogenicity.  It's actually a quite potent carcinogen.  If you go burning a lot of high percentage benzene gasoline in cities you will increase peoples exposure to benzene despite all the pollution controls on cars.