I think it's possible to be consciously in dialogue with other fics, and unconsciously (which if it goes too far, could lead to unintentional plagiarism). I think that the difference between being in dialogue and remixing is that the "dialogue" might be something only the writer can hear - while writing, at least. For example, after reading afrai's Better than Tea (http://thewritegirls.populli.net/afrai/tea.html), I wrote Not Exactly the Galaxy's Greatest Romance (http://thewritegirls.populli.net/afrai/romance.html) as a companion piece to it - it's not a sequel, it's not a remix, it's not an AU, and it absolutely wouldn't exist if I hadn't read her story. Similarly, after reading mercuriosity's Clocks (http://www.heimao.org/clocks.html), afrai wrote Living Arrangements (http://thewritegirls.populli.net/afrai/living.html), which she describes as sort of the red-headed stepcousin of mercuriosity's "Clocks".

I like writing in dialogue with other texts, and papersky has said to me that that is how she wrote at least one of her novels (Tooth and Claw, which is in dialogue with Trollope's Barchester Chronicles). Remixes seem to me to be a different kettle of fish, and I wonder if I've actually done any of them right. This year's attempt I would say was a remix, but I felt it wasn't different enough from the original, though lady_ganesh was kind enough to say that the ending gave her a revelation about her original story.

I think it's also interesting when a writer - I don't want to say "rejects" dialogue, but perhaps, "focuses on an unexpected part of the conversation". When someone, perhaps takes fanon and does something totally unexpected with it, like lady_jaida's Schuldig, who has very recognisable fanon aspects and who is yet perpendicular to those aspects, or bladderwrack's Schuldig, who is not fanon!Schuldig, and is, it seems to me, in dialogue with lady_jaida's.

When it comes to the common fandom tropes, I think it's not just the trope but also the genre - Character X is a vampire will become something different in the hands of the same writer, let alone different writers, if it's written as comedy, tragedy, adventure and so on. Which may also be a function of dialogue - how does this trope interact with genre?