In general I think it is good to reply just to say "no thanks, I'm too busy..."
Most of these invites come from being on a list. You can tell which ones are legit based on some of the content. Also as the kids get older you start to see the coaches watching summer games.
My 2021 kid attended one camp this year, just this past week. We had seen the assistant coach watching my kid's games at a PG - Iowa tournament. My kid hit a walk off to beat a team that regularly places players in the college program that the assistant coach works for. The next day my son got a personalized email saying "I saw you playing at such & such event, that was a clutch hit you had against a good team. We'd love to have you come to our camp so we can further evaluate you & so you can check out the campus." And when my kid wrote him back he got a reply within 10 minutes.
You can tell the difference between something personalized and something that isn't. It was a good camp, my son had a blast, the HC & RC were not only there but were actively engaged in instructing the kids the entire time, he learned some good things, and got more on their radar. Since it is a mid major D1 school, they tend to mostly recruit rising seniors. They told him they are interested, and gave him some specific things to work on before they see him again.
In general getting bigger faster stronger is the biggest priority for my son. But he'll consider going to a camp where there is some legit interest.