1. My head canon is that the "demonic presence" of the vampire saturates the clothes and such so that when the demonic essence breaks apart, so does the rest. In theory, if a vampire had just put on a new shirt or grabbed a brand new wallet from a victim then it MIGHT survive the dusting (and maybe that's how Faith got her own place in season 3, stayed fed and washed her clothes, etc, and also how Angel supported himself in LA without a job). Also, important and magical items sometimes survived, which perhaps showed such things had an aura of their own that prevented the "vampire essence" from saturating them.
2. Oh gods, I could write an essay on the many problems of season 6, and why I thought the writers all grew up with silver spoons in their mouths. Buffy's jewelry and clothes isn't the only thing that was problematic, if you want to show she has money problems with her primary income being an entry-level fast food position. I know some people feel that season 6 is the most realistic, which I believe is simply because the characters became more relatable rather than it being realistic (that is, it FELT realistic as long as you didn't think about it), but it actually broke my suspension of disbelief for the first time to me, because I actually dealt with many of those issues and season 6 just got ridiculous in depicting them, IMO. All I'll say on the clothes is it was probably the fashion industry trying to test or market some new looks (that is, forces outside the story).
I see now that it is going into other issues, but to explore that idea fully is to make my essay which I don't want to do...and I'd find it the most challenging to make that make sense. I think it would literally be easier to rewrite it from scratch in my head than explain away all the stupid stuff they did in season 6.
It would've been really interesting, IMO, to force Buffy to live as Faith did in season 3, on welfare (which even in California is like a full time job, and there are also limits that many people don't seem aware of), and keeping Dawn in school. 'Course others (like Willow and Tara) could no longer live with them then. That would've actually been realistic, unlike what we got.
3. Actually, it seemed to me the writers DID try to show at least a reversal of male/female dynamics if not rape when Faith jumped Xander. I don't want to see the scene again, but seeing the reflection in a TV screen, IIRC, made it really disturbing to me, which I thought was intentional. What was sad is that Xander actually thought they had "a moment." Calling what she did rape of Xander is debatable (I can see a case for and against it), but I felt bad for Xander regardless. (And Faith later telling Anya "I had him first" is just really obnoxious.) The second time where Faith started strangling him would, I think, be classified as sexual assault in unambiguous terms (at least as surveys, polls, and the like count it where even unwanted touching counts as sexual assault, and Faith went beyond that even before she switched to strangling him).
But yeah, since rape is about lacking informed consent (that is, it doesn't have to be about breaking your bones at the same time or using a deadly weapon, it can be drugging a victim, or even imitating someone else in the dark). Of course it's not a case that can be prosecuted given the supernatural element involved. On this one the writers really messed it up, and also made Buffy look really petty to me when she's not even seeing it as rape of herself (which it also was) and of Riley, but instead making her near insane (at least very petty) with jealousy rather than seeing it for what it was.
4. Back to season 6. Same as #2 in that I could write an essay. It was not only stupid, it was out of character. Season 4 and 5 Giles felt bad when he felt he was no longer necessary, but now he's going to force Buffy to sink or swim? BS. And I consider his reasons he gives in the song to represent the extremism of individualism that is romanticized in the United States (though shaped to serve big business, and arguably big government ironically enough), and I'd have hoped that the British would have better sense than that...especially given that Giles is trained to serve in the support role. Nikki Wood had a Watcher until the very end, after all, who then raised Nikki's son after Nikki was killed by Spike.