It's my point of view that the best return on investment for a talented distance runner is to pursue high mileage and high intensity training in HS.
The best return on investment for any distance runner is likely to be a scholarship. The avoidance of student loan debt and the opportunity to compete in college are the likely pinnacle of athletic achievement for the overwhelming majority of "good" high school runners (4:15 mile, 9:20 2 milers).
It's been (reasonably) proven that a high mileage and high intensity approach (80-90+ MPW in Junior and Senior Year) is the best way for most athletes to maximize their performance in HS...which is the way to secure a scholarship and/or the opportunity to compete in college.
To "hold back" to ensure that the athlete continues to develop in college is pointless. The level of competition and talent in college is so much higher that it's difficult to assess which athletes will be successful in college. The best bet is to optimize performance in HS and hope for the best in college.
A slow build of mileage is crucial to ensure injury avoidance, but 80-90+ MPW is the most likely way to achieve a sub-15 minute Cross Country 5k and a spot in the top 15 at Foot Locker or Nike Nationals.