I think it's sensible to buy things now if you know you will still like/need them by next Christmas - what's the point of spending full price in December when you can get them half price now? It's not as if you are going to earn massive interest on the money by leaving it in your account for another 11 months!
I haven't bought anything in the sales this year as I am in a tiny house now, and no room for any more decorations. But in previous years, I have bought decorations in January, especially ones that would be too expensive at full price. I have two of the Lemax ceramic houses reduced by 50%. No way could I afford them at full price, but two years running, the Christmas money I was given covered the cost of them at half price, and I picked ones that aren't 'Christmassy' (i.e. no Christmas trees or door wreaths) so I can use them all winter.