In terms of production quality, sometimes it takes years of iteration on art side and tech to get the look.
You want to nail it down early, but in real life concept artist does the image, artists model and texture the scene and then art director comes back and says, those bricks don't look good. Engine guys say, if we put more polys to make them look good, it is going to kill performance. Then someone says, look we can write this shader using this new GPU feature which is going to make everything awesome, but it might not work. And in any game production, there are 1000s of cases like that, where the thing you want does not exist or you don't have people who have the knowledge. So you just roll into production hoping shader works out and that you are going to hire people who are going to solve XYZ.
Surely that's where getting a production quality level one helps? You really need to know that as early as possible.
You must resist the Siren's Song of rough prototypes. They could be great gameplay but awful to look at. Or vice versa.