There is a mace in the Armory in Dresden that also has a secret secondary function. If you screw off the mace head, it holds a pepper grinder. https://skd-online-collection.skd.museum/Details/Index/288275

It makes more sense when you realise how expensive pepper was at the time. When the Dutch and Portuguese had a stranglehold over the trade, pepper was worth more than gold.

I wouldn't expect gold inside a mace, either. I assume the idea behind the mace, is that it is a novelty. Maybe even the joke was that it was unexpected. I believe that maces weren´t usually in the dinning room, but maybe there was some Kammerherr who carried a mace. It could have also been used to hide the valuable pepper, but that doesn't seem like August’s style.