The rust is fine. It forms a coating that keeps the metal from corroding further by inhibiting oxygen from contact with the exposed metal. As road debris contacts and knocks nicely formed rust coatings, it simply fills in itself and continues protecting.
Due to the thickness of the metal that's not treated to prevent rust, it would take approximately 247 years for the rust to create enough damage for there to be a problem, unless you just don't like the color.
You can always buy something like this, and the color will change.
http://www.eurekafluidfilm.com/about/company.html
'tis what I use.