Actually, I suspect that the only reason for Dooku's existence was so Lucas could (sort of) finish the "Hammer Films" reunion by getting Christopher Lee in Star Wars somewhere...
actually reading the books Dooku's fall was in the works for many years, he was never meant to be a Sith Lord, just a Dark Jedi used by the true Sith, but when Maul died he was the only one left until Sidious could find a real apprentice, he always planned to throw him away.