1) Gavin Dunn (of Miracle of Sound) often uses games as inspiration for his music. In either event, I've never considered it odd to associate songs with characters or scenes.
2) Ah yes, the incest angle. I remember back when I read one between Laguna and Squall (FF8). I remember my author's board and I tried to explain to the writer that the father/son angle was unacceptable. Amusingly, the author's defense was that we were "homophobic," using that as a defense of incest. I just didn't have the words to even start on that one.
On a more amusing note, I recall a scene from Supernatural, wherein the characters are appalled by their fans writing "slashfics."
Dean: "They DO realize we're brothers right?"
Sam: "Apparently, it doesn't seem to matter."
Dean: "...What the hell is wrong with these people!?!?!"
Some of the folks I've asked about the phenomena are of the opinion that "it isn't a problem so long as I'm sandwiched between them." Honestly, I came to terms with that section of fandom long ago. I don't care for it, but I'm not apologizing for something I have no part of.
3) It's actually interesting that an upcoming Twilight knockoff uses incest as a plotpoint (though it ends up being a red herring).
I don't subscribe to such stories, so I simply ignore it. At most, I'll make a joke of the sort that my friends from West Virgina occasionally say. In terms of others liking it, I don't really care, so long as it isn't in any of the stories I read.
EDIT: BTW, when I heard that there were Hawke/Bethany shippers, I just had to laugh, "special hell" moment or not. It's totally wrong, but I just had to sigh and shake my head at it. No use getting agita over it.
On a related note, it's worth mentioning that some fantasies involve the subject being sandwiched in between attractive twins ("I can't die, I've got a date with Swedish twins tonight" - some random anime). A whole extra layer of wrong on top of the incest angle there, though the joke is amusing enough.
4) I have totally written scenes that don't fit with stories I am writing at the time. Sometimes, I'll catalog the scene for later use. If I NEED to include the scene, I'll generally rewrite it,
Case in point, I wrote a "placeholder" chapter in my recently completed story. I knew it was garbage, in that it didn't fit or flow properly. However, it had the skeleton of what the chapter needed to be. I didn't have the passion for writing that scene at the moment, but wanted to move on to subsequent chapters. Eventually, I came back and gutted it.
I kept most of the dialogue, but changed all the scenery that defined the framing of that dialogue. My primary beta read both versions, and told me it was like night and day, which was sort of the point really.
More often, what racks my brain is when I get dialogue wrong, because I have to put myself into certain mindsets on occasion. You may remember that I had to do this with Jack, and to a larger extent, with Aethyta. Their mindsets, while not alien to me, did not operate in a mode that I am generally in tune with.
At any rate, I have a slew of scenes that just felt good at the time, but Lord knows if I will ever implement them. I swear, I could make a short story out of all the random tidbits I have laying around. All I'd need is a good premise to tie all of them together (though it would still be a disjointed mess, haha).