Not buying many gifts is a good option, not buying many gifts because you have a weird rule is not
It's not meant to be a hard and fast rule but it is meant to be a way to help people structure present buying - if there was literally no book my DD wanted one year which will never happen as she's a huge bookworm but there are two "want" toys, then of course I would adjust the system to account for that but I'd probably buy those two mid range presents and then give DD a gift voucher for Waterstones or somewhere where she can buy some books when she does have one she really wants. So on Christmas Day she may not get her "something to read" present but she will have a present related to the spirit of that part of the idea.
Yes it can be an overt teaching tool but it doesn't need to be either ... I have always used this system with my DD, she's 9 now and I doubt she's even noticed that her presents follow a specific "formula" because what she gets is different every year, it's just that they are always items that fall into those categories.
Also my DD will still get a lot - she gets presents from me, my ex, my family and his. By me and her dad both agreeing to stick to this system for gifts from us and trying to get our families to buy just one or two good quality presents each then DD will still get a good 15/20 presents (as well as a few little stocking gifts/sweets/chocolate/Xmas eve PJs) but instead of it just being stuff bought for the sake of buying, they are more likely to be thoughtful (and practical, which BTW is not a bad thing) presents that will actually get used and played with.
Spoiling your child and having Christmas be a teaching event are not mutually exclusive either. Nor does the "teaching event" have to be a boring and negative thing. DD gets a lot of stuff at Christmas so as part of our pre-Christmas preparations I have a day in early December when we have a whole house sort out and as part of that I get DD to go through her toys and sort out anything that is broken/damaged and needs to be thrown away and we choose some toys that are still in good condition but that she has grown out of/doesn't play with any more to donate to charity in order to make way for her new Christmas presents. It's a fun day - we put Christmas music on, we clean the house, we sort stuff out, we put up the Christmas decorations, take the donations to charity and then have a lovely takeaway and movie night.
As far as DD is concerned this is just part of our pre-Christmas traditions (just like the big clearout we have in the summer too), I don't hammer on about how grateful she should be or that it's meant as a teaching moment nor do I force her to give away anything she doesn't want to, but I do encourage her to think about the fact that other kids don't have as much as she does because while Christmas is about the presents and magic for children, that doesn't mean they can't also think of other people as well.