Thanks to the age gap between Capaldi and Matt Smith, the whole "old vs. new" thing is specifically relevant to this regeneration. Smith was dressed in an almost grandfatherly way (tweed, bow tie and braces), but that had the side-effect of making him look like a hipster. This was problematic because the Doctor's costume should never resemble a current fashion trend.
If you can look at the Doctor and say, "That guy looks like he should be hanging out in a vintage shoe shop in 21st century Hackney," then it detracts from his image as an alien -- although of course, if you make him look too alien then you can't take him seriously. Capaldi's costume sidesteps this issue by being extremely simple and pared-down, which I enjoy a great deal (not least because I want to wear the entire outfit myself).
Looking at Clara and the Doctor in the first episode of season 8, the similarities between their two outfits are obvious. He's wearing a white shirt with a prominent collar and no tie, in a more severe version of Clara's lace collar. Then there's the black/white/red color palette, and the fact that he's wearing a cardigan rather than a waistcoat underneath his jacket. If you wanted, you could probably even stretch to linking Clara's tartan skirt to the fact that Twelve has a Scottish accent.
To me, this link between the Doctor and Clara's clothes is a clear sign that intentionally or otherwise, he imprinted on her after regenerating. (Although if you look at Clara's cardigan, you'll see that it's patterned with bow ties -- a callback to Eleven's signature accessory. She's still looking back to the Doctor's previous incarnation, whereas the new Doctor is calling out for her attention.
