Must... resist... temptation to make "Jump the Shark" jokes...
Idea Proposed and Used to Death in the Davies Era: Christmas specials. Gratuitously Christmassy Christmas specials. With snow. Which, unfortunately, look really stupid when they get repeated on BBC3 in July.
Central Premise Recycled From: Go on, guess. Though they're also ripping off Blade Runner visually. Oh, and Torchwood's episode "To the Last Man" (look it up, I'm not summarizing it for you). And "Voyage of the Damned", of all things. And Amy and Rory's outfits are clearly Make Do and Mend.
Reference to Moffat's Back Catalogue: Where to start, where to start...? The Doctor forming a relationship with an adorable moppet in the past and also with the same moppet as a grownup in the future, conversing with a TV picture that's somehow connected with the changing timeline, the Doctor rewriting the story as he goes along by nipping back and forth along his own timeline, airborne sea-life.
Gratuitous Scottish Joke: None actually. I think they may have done with that bit.
Amy Saves the Day with Wuv: Amy and the Doctor appeal to Sardick's Wuv for Abigail to Save the Day.
Star Wars Bit: Freezing someone to pay off debts, plus Abigail's blue hologram-recording.
Nostalgia UK: Space Dickensiana.
Tennant Line: Sardick says "I'm sorry, I'm so, so sorry" to his younger self.
Murray Gold's Festive #1: Well, if you're going to hire Katherine Jenkins, you may as well get value for money by having her sing something vaguely classical.
Inside Joke List: A Tom Baker scarf on Matt Smith, plus photos of Matt Smith visiting the Empire State Building and the Eiffel Tower.
Teeth!: On the Shark!
Item Most Likely to Wind Up as a Toy: Didn't have to guess at this one, as Forbidden Planet London's already got a Christmas box set, consisting of.... Amy, the Doctor, and the Tardis. Seriously? You couldn't give us a lousy Michael Gambon in a bowtie, to say nothing of a pull-the-string-and-she-sings Katherine Jenkins? Or a half a sonic screwdriver? Oh well, go to The Entertainer or Tesco or wherever, spend £1 on a plastic shark and a Santa-and-his-sleigh-set, take five minutes to customise it and you've got your own Christmas Doctor Who toy.
Something Gets Redesigned: Sardick's life.