The prequel was used to:
- Put the Doctor in the place Amy was in The Eleventh Hour (circularly structure)
- Show that the Doctor had found her, he just hadn't realised it
- Be ironic. Clara said that destiny was silly even though the Doctor's idea worked
- Give us something extra
That's all I thought it was. Just a little extra. I just found the conclusion to be predictable. Is Moffat running out of ideas? may sound harsh. But he has definitely used the same themes with different characters.
The prequel is a little extra and the main event is on Saturday night! Now that's what we should get our knickers in a twist for!