There are so many ways to the field. The road can be so curved and variated that i can only recommend you to read on the internet or in books or watch videos to get your answer. But im afraid the answer isnt going to be one and a simple one............wich i guess can be both reassuring and frightening to hear
I have never understood why people ask such questions. I just shake my head and usually place my hand over my eyes and sighs.........because it is subjective. And something like this is very much subjective. I know people who are very hooked on the visuals while others value both and others care fully about gameplay design and story etc. Im a gamer too and i prioritize gameplay before graphics. We are all so different and this is so subjective. One can of course say that the market has a certain "expectation" though.
But personaly i believe it will all work out as long as you officialy state your game's purpose and intention. If it is supposed to have low-end visuals because of stylistic reasons then say that
for my current project i don't actually have a design document because i thought it through and had the image clearly in my head all since 2012. All i have is that, and a partial screenplay and storyboard. The short duration of the game also helps i guess. I also have Asperger's Syndrome wich propably plays a role here but i don't know. Anyway.....i recommend you to make detailed documents anyway anytime, and especially when doing large project!