That's like asking me when I stopped beating my brother.
A) "Beating" can be interpreted as the physical act of abuse or as the consistent winner in eating contests.
B) I don't have a brother.
Being quirky and being a hit in the mainstream aren't mutually exclusive. Quirky is subjective. Mainstream hits are influenced by too many factors to be forecast. Time and taste are fluid. One generation's dreck is another's beloved epitome of literary genius.
Hitchhiker's Guide is batshit cray-cray to some people. Fear & Loathing is so non-mainstream that it moved the friggin' stream to become a hit to a generation not even born in the time it was published.
Don't let marketing and sales decide what you should and shouldn't write. In the era of the self-publishing, there is no such thing as "too quirky." Write the best damn stories you can and make them accessible. Your audience will find their way to you.