Just to clarify, “greying out” isn’t the same as “hiding”. It’s just fading the normal menu icon, so it’s visually different and less pronounced. It still remains visible. You can even have it remain clickable. It’s just a hint to the player that they can’t do anything with the menu item at this time.
I think people not noticing tabs, when they’re obvious icons on the left side, is more their problem than the game’s. No one I’ve shown Highrisers to has had difficulty with that particular design aspect, FWIW. Usually an early comment is “we can make guns?”