Gold Class has a very small amount of cleaner in it (enough cleaner to remove a lot of the original wax). You probably wont get any benefit out of layering it. The best carnuba waxes to layer are P21S, Blitz, Pinnacle. Layering these will give you a little more depth each time. You do have to wait around 12 hours on a hot day before you apply an additional coat.
Your question about carnuba or polymer? With a black car, I would use P21S wax. It's carnuba gives the paint a warm, deep luster with protection for 2 or 3 months. This is a long time considering that Gold Class lasts about a month. I personally use Pinnacle Souveran. As far as looks go, the P21S is a 9.5. The Pinnacle Souveran is a 10 but lasts at most 2 months. Hope this helps.