Hate to break it to you, but even last year, a good portion of the secondaries WERE redundant in relation to AMCAS, and that was when AMCAS wasn't quite as comprehensive. Nearly all of them asked for a listing of the science classes you had taken, and I generally had to relist all my extracurricular activities. The only major difference that I have noticed in the new AMCAS is the optional essay if you consider yourself "disadvantaged" and the practice vision essay, which only a few schools asked about anyways (I completed 15 secondaries, and I think maybe 3 of them had a "practice vision" question). AMCAS is also more detailed in asking about activities, but I don't think that would change the secondaries that much.
In general, secondaries will ask you a very open-ended question such as "Include any additional information you think would help us in evaluating your application;" some ask for biographies; some ask you to describe moral/ethical dilemmas; some ask you to describe a specific struggle or difficulty you overcame; some ask you to describe a meaningful or significant event in your life; and then of course somewhere in your secondary, it's always a good idea to fit in why you want to attend School X, if they didn't already specifically ask you. In general, after you've done 3-4 secondaries, you should be in good shape to complete the remaining ones using parts from the different essays you've written.
