I understand your point, I just disagree.
I do think books are great gifts, and if people ask for suggestions, it could be suggested. I just think that gifts are the choice of the giver and you can accept them graciously (which is also a great thing to teach kids!) without it automatically meaning you will have a cluttered house and spoiled kids who don't value or care for posessions. Those are organization and character issues that are my responsibilty to enforce daily as a parent in my home that I don't see as directly related to accepting a gift that is generously offered in love. For instance, at our house, when little J gets a new toy, then he chooses another one to donate. And it's my responsibility to enforce how he manages and appreciates what he has.
I think your third sentence hits on a heart of the issue...we as parents worry about (validly so) about the types of relationships our kids have and how they are defined and specifically whether receiving gifts of a certain quantity or quality will affect them negatively. I just happen to see this "we already have too much stuff" logic most often applied to the gifts of former foster parents and birth parents when in reality it's the relationship that's the discomfort. I think limiting or directing the gifts from that person is a way of exercising control over the relationship. If it's an inappropriate relationship or truly inappropriate gift, then I totally support that. If not, I think we should allow people to give from their heart, say thanks and continue to teach our kids character as we would anyway, with or without that one toy, piece of clothes, etc.
Just my opinion.