I'm not ashamed to admit I cheered at page 21. Awesome. (Yes, I am a fan of Nanoha style "cool your head" methods)
Of course, Vita getting "corrupted" or whatever towards the end makes little sense, given how she's a sentient magical program not a human. She should be even more immune than Lich-girls.
Poor Vita is always there to show that the bad guy means business. Considering how the self repair system the Book of Darkness had fot it's Knights no longer works since Hayate became it's master, perhaps the Wolkenritter has now more human-like weaknesess?