The answer to the question should be based on how much would a PC be charged for access to a similar work. Of course that's based on how rare such texts are, hence the subject of the thread. What I'm saying is if you set the availability of high Q texts low then that raises the value of creating a character that is a good writer proportionally.
Also if your publishing for trade good writers might not even bother to use skilled craftsmen and resonant materials. Let the customers add their own after market modifications.
It may be troupe discretion but it should be tied to what you make the characters go through to get good books. Since the payoff should be proportional to how good a writer they are, if it's established that good books cost a lot of vis and/or adventure then creating a really good writer makes plenty of sense.
Selling down a few stats it's basically three minor virtues to start with Com +5 and Good Teacher. Or you could go with an Essential Virtue that applies to writing, and for one major and one minor you can get an effective Com +6 and Good Teacher and you don't have to sell down any stats. What would you expect PC's to do to get access to such a writers books. That's roughly what a player who makes such a writer should rightfully expect from NPC's who want his character's books.