Well, for me the "death of the author" stuff only applies so far as the recognition that we don't have perfect access to authorial intent--so we have to guess. In most or even all of the high-profile cases where an accused plagiarist used work from a source from outside fandom, she always claimed that her intent was to pastiche or homage or whatever. The thing is, the fans didn't believe her--and sometimes for good reason. And so, like all interpretation (I would argue), it ends up depending on a readerly construction of authorial intent.

but this kind of literary allusion assumes so much between reader and writer, you know?

But this is fandom--glorious collaborative intertextuality, queer female space/minstrel show, slash the slasher, writing porn is like baking cookies, community of readers who are also writers fandom. If that type of assumption can be made anywhere at all, it's here.