I always felt that the story of Plagueis was yet another sly reveal as to Palpatine's real identity - for those viewers who were discovering Star Wars through the prequels. True, in an earlier draft Palpatine reveals himself as Anakin's father but Lucas wisely re-wrote that (we only need one "I am your father" in the saga, after all).

I don't think the character should have played a bigger part in the films anymore than I think Dooku should have been in Episode One or Grievous should have been in Episode Two.