Some belated thoughts, as threatened promised:
Buffy's still a hero. (She's still my hero.) And this is still her journey.
Spike would never have done what he did without the Buffy-effect. That tells me a hella lotta about Buffy, and her journey.
My problem with the climax isn't so much that Spike got to share the hero's journey (although I do have one). I had the same problem with "Grave," and I don't begrudge Xander his triumph the way I begrudge Spike his (and that latter is My Personal Issue): despite the strength of the ensemble, this is a show about an individual's hero's journey, and I think--as a *structural* reinforcement for the emotional themes of the season--that individual should get the action climax of the season, and in fact the action and emotional climaxes should be the same.
This is why "Becoming 2" works so well for me, and why as much as I love S3, "Graduation Day 2" doesn't work as well as "Graduation Day 1." In "Becoming 2," *everything*--emotional, thematic, action--climaxes in that cross-cut Buffy/Angel - Willow-spell - Xander rescuing Giles scene. In GD1, the emotional/action/thematic climaxes are all in that Buffy/Faith confrontation. In GD2, the emotional climax is the Buffy/Angel drinking scene and the action/thematic climax is the graduation. It's weaker than I expected (and those weeks waiting for my bootleg probably hurt it as well).
In "Chosen," the thematic and emotional climax of the season is the "Every girl is a Slayer" montage. But the action climax, it feels to me, *isn't* the girls fighting the ubervamps, it's Spike destroying Sunnydale. And it makes me grumpy (still!) because in a show called Buffy the Vampire Slayer, I want Buffy to get the Big Moment. In a show that ends with a vision of female empowerment, I want the Big Moment to be that empowerment--and not the male destroyed happily by channelling someone else's power.
Unrelated: thanks to Quotable, I've been thinking about Buffy's big speech. "I hate this. I hate being here. I hate that you have to be here. I hate that there's evil. That I was chosen to fight it. I wish, a whole lot of the time, that I hadn't been. I know a lot of you wish I hadn't been either. This isn't about wishes. This is about choices."
I like the implicit contrast between what the vengeance demons (specifically Anya) did and what Buffy is doing, the contrast between the horror that came from wishing but being unable to claim power and the hope that comes from being able to choose, to do so.