It looks like most of your questions have gotten definitive answers, so I’m just throwing in my two cents on some general issues. You’ve asked for opinions, and I’m a highly opinionated woman who found your questions thought provoking, so this is going to be long. Sorry!
Fanon
-How do people feel about using fanon?
Fanon is just that, fanon. It isn’t canon, it’s not carved in stone and a fanfic writer is under no obligation to follow it. Hell, fanfic writers freely ignore inconvenient canon, so why should we hold ourselves to fanon conventions? And, at the same time, just because some people don’t like a particular fanon, doesn’t mean you have to avoid it if you find it believable and if it serves your story.
What it boils down to, is, write what seems believable to you. Whatever the canon or the fanon, if you are writing a good story, you’re going to draw readers in, and they aren’t going to care about the fanon details, one way or another. And, if they do normally care about those details...they’ll get over it.
-This is a much debated topic, but is there even a marginal consensus regarding the age of Spike?
I didn’t know there was a debate. One caution for those who point out that a real Victorian mother wouldn’t be worried about a 25 year old man being unmarried: Joss has admitted that he sucks at research. He also sucks at Math, but that’s another story. William’s mother’s acceptance of his bachelor state proves nothing about his age. Since there’s no firm canon on his age at turning, my advice is to write Spike as the age you believe he was. If you are doing your job as a writer, your readers will follow where you lead. (And, in my experience, you are doing your job as a writer.)
-Buffy smells like vanilla in a lot of fics. What's up with that?
I’d seen so many references to that in fic that when I started writing, I included it, assuming there’d been a scene in canon that I’d missed. I still use it. For me, Buffy likes to be feminine, but she’s also pragmatic. I can see her using a clean, light scent like vanilla in preference to a cloying floral scent or a heavy spice scent either of which vampires can probably smell a mile away. And, here is where I strongly disagree with a2zmom, who has pointed out that vampires would be able to smell Buffy’s soap, shampoo and deodorant, and assumes that these things would necessarily be different. Speaking for myself, I use unscented personal care and laundry products. If I want to use perfume, I have soap, body lotion, and dusting powder in the same scent, and I’ve been known to finish off my hair with a rinse of cold water into which I’ve placed a few drops of perfume. A vampire sniffing me would not get the olfactory variation that accompanies use of a variety of differently scented products: just my favorite perfume and my own body chemistry.
If you want to give Buffy a perfume, give her whatever perfume you believe Buffy would wear. Coordinate it with her shampoo and soap or not as you please.
Chiming in
Fanon
-How do people feel about using fanon?
Fanon is just that, fanon. It isn’t canon, it’s not carved in stone and a fanfic writer is under no obligation to follow it. Hell, fanfic writers freely ignore inconvenient canon, so why should we hold ourselves to fanon conventions? And, at the same time, just because some people don’t like a particular fanon, doesn’t mean you have to avoid it if you find it believable and if it serves your story.
What it boils down to, is, write what seems believable to you. Whatever the canon or the fanon, if you are writing a good story, you’re going to draw readers in, and they aren’t going to care about the fanon details, one way or another. And, if they do normally care about those details...they’ll get over it.
-This is a much debated topic, but is there even a marginal consensus regarding the age of Spike?
I didn’t know there was a debate. One caution for those who point out that a real Victorian mother wouldn’t be worried about a 25 year old man being unmarried: Joss has admitted that he sucks at research. He also sucks at Math, but that’s another story. William’s mother’s acceptance of his bachelor state proves nothing about his age. Since there’s no firm canon on his age at turning, my advice is to write Spike as the age you believe he was. If you are doing your job as a writer, your readers will follow where you lead. (And, in my experience, you are doing your job as a writer.)
-Buffy smells like vanilla in a lot of fics. What's up with that?
I’d seen so many references to that in fic that when I started writing, I included it, assuming there’d been a scene in canon that I’d missed. I still use it. For me, Buffy likes to be feminine, but she’s also pragmatic. I can see her using a clean, light scent like vanilla in preference to a cloying floral scent or a heavy spice scent either of which vampires can probably smell a mile away. And, here is where I strongly disagree with a2zmom, who has pointed out that vampires would be able to smell Buffy’s soap, shampoo and deodorant, and assumes that these things would necessarily be different. Speaking for myself, I use unscented personal care and laundry products. If I want to use perfume, I have soap, body lotion, and dusting powder in the same scent, and I’ve been known to finish off my hair with a rinse of cold water into which I’ve placed a few drops of perfume. A vampire sniffing me would not get the olfactory variation that accompanies use of a variety of differently scented products: just my favorite perfume and my own body chemistry.
If you want to give Buffy a perfume, give her whatever perfume you believe Buffy would wear. Coordinate it with her shampoo and soap or not as you please.