Correct, there's an audience for everything, even Mary Sues. So, why not leave it up to the reader if she/he likes it?
Maybe the following should be included into this thread:

What does the author want to achieve? which are her/his goals?
Share imagination?
Send a message of whatever kind?
Describe a world and its inhabitants?
Show the development of a single char or group?
Humour? Suspense? Love? History with facts or simply free imagination? Tragic? Technic?
Win a literature prize? (Gee, how many of them did I have to buy and saw them rotting in the shelves <img src="/ubbthreads/images/graemlins/delight.gif" alt="" /> )
Which audience to target? Age, gender, genre preference

I read this thread with interest, but I really missed the audience. And I think, they play a very important role - for those authors wanting to show their work in public, of course (publish or post) - they play no role at all for those simply going into interaction with themselves (private writing).