I don't believe that speed limits being too low is the primary cause of people following too closely. The primary cause of tailgating is poor driving habits. Most drivers that tailgate will do so REGARDLESS of the prevailing speed of traffic. They either don't know any better, are not paying attention, or are just raging a$$holes (mostly this).
In fact, it is my opinion that raising the speed limit will actually increase the incidence of people following too closely, because most drivers don't seem to have a CLUE that following distance should increase as speed increases.