Thanks for posting. So I think you'll discover that your approach, history and results are not that unique. Actually, I found myself reading your post and thinking..."yeah, I've been there and I remember going through exactly that". Nothing you posted surprised me at all. I'm not sure you know this but, getting recruited to play college baseball at any level is ridiculously hard. Listen, my kid was the second-to-last kid on his national travel team to commit. Guess what? I learned years later that being recruited second-to-last from a successful travel/showcase team is not necessarily a bad thing. Because he was also one of the last kids from his travel team to be playing in college after 4 years. The kid that was recruited last on his travel team had a very successful college career and is still playing in the minor leagues. So, think about that for a minute and the reasons why. Recruited = Passion + Skill + Persistence + Exposure + Luck.
College Coaches are looking for kids that can solve their problems. They need a reason to "invest" in a kid either with scholarship money or help with admission. Your son has received interest and that is a very good thing. You understand the mechanics of the process. It is also a signal you are doing the right things, so keep at it. The next level is "serious interest" and you'll probably know that when it happens, because when it does it happens very quickly. Remember, college coaches need a reason. Try to understand things from a college coaches perspective, and this may help you and your son.
PS..I agree with Smokeminside and 3/2 that an ACT or SAT tutor may be beneficial. Again, anything to bump his standing in the coaches eyes is always a good thing.