The thing is, it is addressing a real problem, which may not be obvious to those posting here who take a more religious view of Christmas in their family celebrations.
OTOH, it has become common for families to rack up significant credit card debt during the holidays; people getting trampled at places like Walmart seems to be a yearly event; and I know many families of young kids who struggle to no avail to reduce the number of gifts their kids receive to something that they can at least fit home in the car. These children are getting up to a hundred gifts, and are sometimes left in tears when the family insists that they keep opening for hours.
I actually think the Advent Conspiracy idea is well thought out on a number of levels. The idea of buying only one less gift (not only one) is doable for most, it makes people stop and think about what they are doing when they buy, and it isn’t so wild that people will just be turned off.
Secondly, Advent has actually pretty much disappeared, even among many Christians. The Christmas season begins right after Thanksgiving in the US, or Halloween here in Canada

. There is no concept of a lead-in where we contemplate our need for a Savior, that includes things like fasting or extra prayer. To bring back some real observance of Advent in at least various CHristian groups would be a good beginning.
As for the conspiracy bit - to some extent I am sure it is just meant to be catchy and intriguing, and perhaps a bit of a joke. But OTOH, the message of the Advent Conspiracy is very counter-cultural at this point in time, one that is little seen in our larger culture. The vast majority of messages we see about Christmas are related to consumerism and buying. These things are presented as being fundamentally tied to the Christmas message of giving, but of course the level of consumerism we see today is far beyond anything that has traditionally been a Christmas custom.