I definitely got the idea that Anya was supposed to be unconsciously picking up the vibe between Xander and Spike, so your intention translated there. Her annoyance is appropriate, her commenting on it in-character, but the sound was just not quite right. I hope I'm not raining too much on your parade; I maintain that you're doing a great job.

I agree that Spike is ahead of the emotional curve, and that he's been (to some degree) aware of his feelings since their first encounter. That's very in keeping with canon, but he's also someone who pays lip service to denial of his own feelings, which adds another layer of legitimacy to his defensiveness and surprise, for me.