If he rows/intends to row at Navy, definitely attend. Our son rowed in HS and attended a rowing camp at Navy before his senior year and was so impressed. Navy was attractive to him just based on the strength of their team and the crew facilities. In the end, he chose Army and rowed there, but Navy has the better team.
No experience with Junior Day but can’t see how that trip wouldn’t be worthwhile to a potential rower. Enjoy.