The prepcast is going to help you understand the concepts and key points. Just doing the exams is a memorization of questions. To be honest I've done the "exam only" method years ago for Microsoft Certs. This was a common practice 20 years ago, which is why the PMP is the way it is. It's very situational and intentionally built to circumvent memorizing questions. The questions, while close to the real thing, are not exact. I believe that is intentional as PM Prepcast can get into trouble for copyrighting the actual questions from the exam. (don't hold me to that) I can say that it does help with both learning some concepts, as well as, how to pace yourself for the real thing. Skipping the Prepcast videos will absolutely leave gaps in areas as the practice exams will not cover everything. if you are scoring that high, it sounds like you have a good grasp on things already.
All that being said, pick a topic you think you could strengthen and try a video. If you think it's not helping go back to the exams. If you are picking up new things you aren't getting in the exams, stick with the videos.
