Echoing Others:
Buyer Beware!
First time we got one of those camp invitations after a showcase, we were excited. It seemed so encouraging. But then I actually wrote to the coach who sent it. He said that while he had seen my son at the showcase and liked a lot of what he saw, they were not actively recruiting him at that time. He was frank enough to say why -- the kid was too physically underdeveloped for them. (he weighed a whopping 125 lbs at the time.)
But he also said that he looked forward to seeing him at their camp in the future, since he expected him to develop physically by the time he entered college.
Eventually, because this school was actually a school in which my son had some interest and thought might be a fit academically, he went to a camp there. He actually performed quite well at the camp -- so much so that they contacted his then HS head coach and came to watch him play during the summer.
Unfortunately, the kid had his worst performance of the summer when they were there. But they did seem him again at a multi-school event at which he performed much better. That was late in the recruiting season, but it did seem to get him back on their radar a bit. Eventually, though, they went in another direction and so did he.
Long and short. Coaches send out these kinds of follow up letters to lots of players, almost in blanket fashion. Doesn't necessarily mean there is any particular interest in your player. Sometime if you press them, they will come clean about that. Sometimes they will be evasive. Since one gets so many of these things, we generally ignored them, but if they represented a genuine possibility, we pressed the question with the coach of whether there was particular interest in my son. Mostly the answer was no or evasive and we just moved on.
On the other hand, if it's a school you are interested in, getting in front of them at their own camp can sometimes be a good thing. Not always. But sometimes. Actually I would say rarely. I say that because it's pretty hard to stand out even at these school specific camps. Usually there are man, many more good players present than they have spots for. Plus usually completely independently of their camps, there are prospects on their board that they have been following. And they aren't really all that interested in what gets thrown over the transom, as it were.
That's not to deny that may hope to find a player or two through their camps. That's partly so that they can say in their marketing materials "Every year, we sign players from our camp." I mean if they couldn't say that, how could they market these things as being in the player's interest at all? So it's not like they are opposed to finder players though these camps. (Plus, in fairness to them, some of the schools may not have tremendous recruiting budgets, so anyway that they can see more players is a plus.)
What they don't tell you is that the number of players the recruit via these camps is probably easily dwarfed by the number of players the recruit in other ways.