I always thought that they should have somehow made a connection between the First Evil's motives in trying to kill Angel in Season 3 and its using Spike in Season 7. The only times that it shows up in Sunnydale, it targets a vampire with a soul. There should have been some special significance in that, and, even if there weren't, someone, Giles, most likely, should have at least mentioned the possibility.All I can think of is that this was merely a way of justifying why the First hadn’t tried taking over the world before.