2 follow-up points:
Don't make the mistake of thinking that your odds of getting drafted are better at one school vs. another. There are plenty of MLB players from schools that you may never see in Omaha. The much-ballyhooed Stephen Strasburg pitched at a mid-major program. He was not regarded as the biggest prospect coming out of HS, but he got on the field and therefore had a chance to work his way up the ladder. And I can assure you, by the end there were plenty of pro scouts hanging around when Friday night rolled around, I don't care who the opponent was. We saw a similar phenomenon in VA some years back with Verlander at ODU. I would hazard to guess that the odds of making MLB are the greatest at the school where you have the best chance to play either every day (offensive player), or to pitch in the weekend rotation.
Second, if you feel your son is still looking at this starry-eyed, 17 is not too young for you to tell him to snap out of it and start making decisions like an adult. Yes, kids have always done this. Time was when parents would always make them stop doing it, if only for their own good. For some reason, in the last decade or so, parents seem more willing to indulge the prolonged adolescence. Your son would profit from your taking the more old-school approach.