How High Can A Grade Go With No Luster?

So, I was thinking. If you have a coin with some breaks in the mint luster, it tends to really show up during photography. From what I've seen, this is seen as a detriment most times. If a coin has no luster left, but is clean as a whistle, how high can it possibly grade? Sometimes toning can make a coin look beat up also, but that doesn't detract from the grade, so why does mint luster.

Forgive my ignorance if this is an obvious question/answer.....