Many of the critical items in the game require gears, and in many seeds/worlds they are incredibly rare. This presents an issue as it may take you several hours of gameplay to understand that the world was generated with very few clockworks (the only predictable way to get gears).
In addition to tumbleweeds and graves I'd suggest adding some other mechanic to make or discover gears. Even if we came up with some method to build stone gears or something that needed to be replaced over time (eg broken fridge / flingo).
As a fallback allow gear frequency to be set as a server option, either in general terms or a basement threshold.