ross, I agree with you that it's starting to be a bit late at the top 12 to start developing potential. I don't believe that those who had three bad weeks in the semis (Katie, Paige, and I'd personally throw Lacey in there) will really start to impress because they made the top 12. I still have no clue how these three girls made it through.
In season 7, when they had the same format for the semis, both Archie (with Imagine, top 20) and Cook (with Hello, top 16) had what the show calls "moments" And they ended up winner and runner up. I'm not sure I'd call a "moment" any performance we've seen until now. Crystal has been consistent and professional, but I don't believe she delivered a "moment". Big Mike's performance this week was loved by many, but hated by just as many people. I wouldn't call that a "moment" either. This season is lacking excitement big time. If no "moments" are delivered in the next two weeks, I'll start calling this season utterly depressing.
ETA: My definition of "moment" is probably not the same as Simon's. I'm talking about a performance that has everyone talking and in a positive way. Like Heartless for example. I was watching it again this week and I was like "that was exciting"!!