Thanks, such a wholesome article! How about you approach marketing your game as if you were building a cult (following).
I can share my professionally hard-worn wisdom that GDDs (game design documents) are a very sharp sword, with two edges. The edge facing towards you might be even sharper than the other one. You want to coordinate with others and get on the same page. And writing something down can be a great help to sharpen your vision. Game Design also often involves making calculations and writing texts. These are also called GDDs, but they approach game assets (as what you're writing will end up in the game).
However, GDDs have a sort of uncanny valley. They can be good to get a general gist or direction. But that's best left vague enough to be conveyed by talking about it. And they are good for some detail work (i.e. an excel table with actual calculations).
Overall though, I would strongly advice against them. In a company, they signal an unhealthy managerial style, can prevent you finding out what's fun, and are also often times very misleading as two people can interpret the same document in three different ways, especially the bigger it gets. It's a good idea however, to document the obscure elements of your workflow and game somewhere.
As you point out yourself,
iterate, iterate, iterate. You'll want to have a general direction and goal, but then take it one step at a time.
Good luck!
