Congratulations Newcomer. That means he's on their radar...a very good first step.
They've probably sent the same invitation to dozens of potential players. I would go if you can...get to see the school (you are from the top half of the state), nice weekend away, meet the coaches, get a feel for the atmosphere.
It also demonstrates your son's interest in return...a good thing if USD is one of his choices.
Have fun and good luck!