I completely get about needing to spread the cost. There are two things that in practice would always go wrong for me.
One is that people have this really annoying habit of either changing their mind about what they want, or even worse, buying it for themselves in September. There are some people that like stuff that you can repeat, like bath stuff, but it's different with a specific toy, or book, or DVD. So I worry that what I get will be superseded. Or, as others have said, forgotten in a cupboard somewhere.
The second thing is that not having quite enough money does stop the madness a bit. I like Christmas but I fight every year to keep it reasonable. As a child we had very simple Christmases and when I was a young adult I remember having a £5 limit per person because not all of us could afford to do more. I don't think it occurred to us to make it a higher limit by spreading the cost over a whole year. Christmas was a seasonal thing and you only spent on it what you could afford that month.
So I do wonder a bit about whether we would all have just as much fun if we didn't spread the cost, and just spent maybe two months worth of "spare" money, ho ho. And I know that for some people, two months spare money isn't a lot. That's kind of my point- if money is tight, what are we all thinking, saying that all our spare money for more than half the year ought to go on this one thing?
So not sure how U the OP is.