Seriously... 'distinctive voice' or not, would any author want to be thought of as, "Oh, she's the one whose grammar stinks"?
Well, I wonder just how well Mark Twain's books hold up in that regard. I suppose it all depends upon whether the notoriety translates into sales from. I've run across plenty of literary specimens in the past that were lauded as "great works" that didn't contain "good grammar" at all. In fact the authors went out of their way to NOT have good grammar. It all depends on the interpretation and what's "in" at the moment.
That and whether ultimately they tell a story that grabs the reader's attention and won't let go of it.
Beverly