I think that Anakin was neccessary to carry out the plan. Palpy needed somebody that would throw the other Jedi off their toes, and just really confuse them and break their hearts. Now I am a huge Dooku supporter, but the Jedi already knew that he was an enemy (though I'm not sure if they knew he was with the Sith). His betrayal had already been completed a la AotC, so they knew that they would have to face him. Now Anakin is a complete surprise, and keeps the Jedi off balance, having to deal with the feelings of his treachery.