Here’s my take, for whatever it’s worth. These are money-making enterprises, and they do everything they can to give the impression that your child has received some wonderfully prestigious honor, when in fact, as you correctly ascertained, they send out their mailings to lots of kids. So, the part about their operation that bugs me is they try to give you the sense that to ignore them is to forego a tremendous opportunity/accolade. It’s not, and if what they offer doesn’t feel worth the significant price they’re asking, feel free to pitch it in the circular file.
That being said, kids do go to these things and at least some of them seem to have good experiences. If the description of their program sounds like something that would genuinely interest your kid, then I recommend googling the program in question and seeing if it sounds like it’s a worthwhile use of time and money. You can probably find specific threads here on CC and elsewhere.