Congratulations! That’s definitely a confirming score, 1960 and up. (It does not vary based on your child’s PSAT score).
The only reason to take it again would be if he’s going to apply to scholls where a higher score might help him to get admitted or to get more merit aid from a school (not part of National Merit).
If you’re talking about the National Merit scholarship process, those are usually tied to special areas of study/interest, parents’ employers or by specific colleges (they’re not very much money – couple thousand.)
However, some schools offer free tuition and/or full rides for all students with NMF status. The actual score on the SAT does not matter for those. Simply becoming NMF gets you that. (I’m talking about schools like Oklahoma or Alabama for tuition+board, and Forham for tuition. There are many others).