Agreed. I don't know why they didn't choose to have DB show up as The First, far more interesting than how he showed up in End of Days/Chosen.
Although I get why they did it. They needed to show us how Spike changed.
That Spike would stick by Buffy, sacrifice himself, regardless of her feelings for Angel. It was basically a test for Spike. But it did come with a price - it made that last sequence in Chosen a tough sell.

Also agreed on Xander. I think they should have killed him off early on and let him be the First. That would have been kickass.