I remember that the First evil said that it has still some plans with Spike and that's why it didn't kill him. But I think he had never this important occurs. May I missed something I just can't remember me! I think the First evil said it after Spike had lost his trigger? Or was it before? Was the trigger the thing which the First evil meant with the important role of Spike? But I think it was after the hypnotic-Spike part. In contrary in the end it was Spike who rescued Buffy from the edge and who destroyed the army and the First evil!