I know, and it says that happens because it will be replaced by an event specific currency. I think it's a bug in the coding, because otherwise it's a major game design flaw and the rest of the game is too well designed for that. I wish there was a way to contact the developer to report it as a bug.
The coctails are used for quickly rebuilding a new setup after tearing down an old one. Essentially it is a respecialization currency. But it only saves construction time, you still need the materials. It is the weakest major event currency I have seen so far. But ALL major events have topaz upgrades so it is not a bug, this game expects you to play it for years so you will buy the topaz upgrades bit by bit each year.