This is a really fascinating post. For me, the thing about intention is that it's hard to do without it -- I don't necessarily read with the conscious goal of decoding an author's intentions, but I do read as though those intentions are somehow manifest in the text and relevant. And even the parts of the text that might not result from imputed intention (your example of the dead lesbian/crazy lesbian trope) still come across to me as though they should somehow reflect on the author -- that a text could be read as the sum of the author's intentionality and unintentionality, and that both are significant.

When I think about it, I approach intention in television shows differently than books, because TV shows seem more like the product of a collision of multiple "intentions" (producers, writers, directors, actors, and really everyone else involved to varying degrees) that aren't necessarily coherent or compatible or entirely consistent. Though I probably approach movies more like books, because they seem to tend towards a more unitary vision, even if that's a myth and they're more accurately described as corporate productions made by committee (at least the ones made by big studios).

As for interpretation in fandom, I wonder if one additional reason -- beyond the ones that you list -- for why a particular interpretation might achieve a following in fandom regardless of accuracy is because it's especially productive in generating new stories, discussion, speculation?