This question has been asked hundreds of times here. And the answer to your question is NO. It is certainly not necessary. During this summer, I had 7 coats of Klasse SG with no carnauba topper. I was very pleased with the results. It looked nicer than practically every car on the road. Now a carnauba topper does help though. It does give your finish that special something. It gives your car some warmth and depth.
What I and others suggest to most is to first apply a few layers of the Sealant Glaze. If your happy with the appearance and feel of your finish, then just leave it at that. Now, if you want to experiment a bit, then apply some carnauba to say the entire hood. Then judge for yourself if you like the look. Trust me, you will like the look. If you don't want the carnauba then just give the hood a Dawn wash to remove the carnauba. Hope this helps. Laters.
