Johnj,
Keeping your mouth shut and letting your son's talent do the talking is the no-brainer part of your job. Frankly, that's what most everybody tells someone who asks this question, and it shouldn't require much thought.
But I'd urge you to listen more to the posters here who are trying to communicate a more important message to you:
Stop viewing the HS baseball program as being there solely for the purpose of developing YOUR son when he comes along. Your son should understand that his job is to go contribute to that program, to make it better in whatever way coach needs him to, and to help the others around him succeed. It may be that his most important job is to be on JV, to develop his skills along with the others on JV, and let those Juniors and Seniors who have more experience take on the other Varsity players in the district. Being a contributor to a winning organization is the REAL learning experience, and that's where he'll get the most valuable personal growth.