Because the Doctor is eeeeeeeeevil. I keep saying it, but no one believes me. 
So he would recognise the new memories immediately, and for what they were, to influence his character soon enough to save the starship.
I don’t buy this argument. If he didn’t realize that his life had changed, wouldn’t his character be influenced just as much? Or more, considering that he’s a stubborn SOB and would probably try to ‘dig in’ as much as possible as soon as he realized that the Doctor wanted him to be changed?
On the other hand, I don’t really want to nitpick that sequence to death. It was funny and good television, even if it didn’t make that much sense in terms of the Doctor’s motivations.
Actually, come to think of it, it does make some sense in terms of the Eleventh Doctor’s personality - he’s occasionally flamboyant and tends to do certain things just because he thinks that they’ll be cool - like going down a chimney on Christmas Eve. “My whole brain just went ‘what the hell’”?
Well, I saw it last night and liked it very much. Just the right amounts of cheese and irreverence.
“Sorry about the picture quality, I had to recover the data using quantum enfolding and a paper clip.”
RE the Star Trek reference, yeah, that was pretty overt; when the lackey told Kazran about the impending crash he referred to it as a “Galaxy class ship.”
I’m just wondering about Abigail’s family’s reaction to finding out that after he turned down their petition to spend Christmas with her, he went and hogged the last bit of her life having Christmas with her himself.
I loved it–silly but funny and fantastical. The frozen girl was really beautiful–like, woah! 
The references to Einstein and Marilyn and Sinatra were fun. Michael Gambon is always terrific.
I really liked the bit with the psychic paper when the Doctor first meets the young Kazran.
Kazran: Are you really a babysitter?
The Doctor: I think you’ll find I’m universally recognized as a mature and responsible adult.
(The Doctor holds up the psychic paper for the boy to see)
Kazran: It’s just a lot of wavy lines.
The Doctor: (looking at the paper) Yeah, it’s shorted out–finally a lie too big.
it was… okay. not moffat’s best this year, but passable. i thought ‘vincent’ and parts of ‘the lodger’ were more interesting.
i did like the shark pulling the sleigh. that was pretty cool.
otherwise, sorry, gang, but i miss not only tennant, but eccleston. i’m watching, but smith is never gonna be a favorite for me.