This is a reply to both comments - I see where you're coming from, but personally I just happen to disagree. See this thread from my Intervention essay which says most of what I think about those last moments (or rather, why Buffy smiled).

And I think that giving Spike the amulet was the biggest compliment she could have given him - can you imagine if she'd brought Angel home: "Well everybody, the Champion is here!" That would have been worse I think.