Why would Buffy try to fight an end to the world? For she knows, by now, surely, that if she dies, she'll return to heaven, a place she longs for and knows about since she's already been there. "Crawl out of your grave you find this fight just doesn't mean a thing..." And she's right.
This is probably why this season has felt fairly anti-climatic. If Buffy dies again, it's no big deal. If I knew I was going to heaven, I don't think I'd care much either.
Plus, I think I'd start to try and re-summon the spirit of the First Slayer who would seem to be a match for the UberVamp and the First Evil. If Buffy could be super Slayer in Season 5 after a spell like that, how could the Uber Vamp even stand a chance?
Don't get me wrong...I think this season has been the best in a long time. One of the reasons I loved the first three seasons of Buffy was the music and the Bronze (though I'm not quite sure I like the re-modeled Bronze as much) and how it permeated Buffy. We caught glimpses of the Bronze and its unique music in Season 4, 5, and 6 of Buffy but it wasn't like the first three seasons. Season 7 has brought it back with a vengeance...am I the only one hoping for a couple of new Buffy CDs as a result? Especially the track from CWDP.