Basically, what I want from the stories I read is for them to be as true to the show as possible. A really interesting part of writing a slash fic (or any unconventional relationship fic) is justifying why these two (or three...) characters ever got together.
So Xander Wishes was mostly just about me trying to give Xander more depth and insight than the writers usually allow him. (And *so* tempted to go off on a rant here, but I'm not gonna do it. Not!) Also, I put a bunch of my thoughts on vampirism and Angel specifically in Xander's head.
But then as the story progressed it went somewhere I never gave it permission to go. Suddenly Anya was there, and Xander had a death wish, and then he started thinking of Halfrek...
I don't remember what I'd actually had planned for the ending. Maybe nothing. I pretty much suck at endings, so I often just don't think that far ahead. But I like the way this turned out; it had me thinking sequels.
And when 'Waiting in the Wings' aired, I really had this whole idea for a sequel where Angel examines his feelings for Cordelia and realizes that she gives him a feeling of being seen (a la Spike in 'Fool for Love'). But he thinks maybe though she wants to see who he really is, she can't because she wants to believe certain things about him that just aren't true. So Angel thinks that maybe his feelings for Cordelia come from the way she reminds him of Buffy... but he eventually realizes that it's actually Xander she reminds him of, Xander who truly saw him, understood him. So Angel starts having all these warm fuzzy feelings, and he's holding baby Connor in his arms, and all is right with the world... And then his soul takes off.
So Xander would get his wish, but the vampire he gets is Angelus, not Angel.
That was my plan. But it's gone now, 'cause besides Cordelia losing her cool, and the very dull Gunn/Fred thing that was happening there, I really liked season 3, and wouldn't change it.