Empirically speaking, we already overspend on Grad and PhD students. We overspend on most sciences (because they’re psuedosciences) and underspend on those that matter (physics, material science, chemistry, biological chemistry, genetics, archaeology) Virtually all other programs (psychology, social sciences, political sciences), and certainly all pseudosciences (the humanities) are a waste of money.
Even in those hard sciences we can see in the cites that the number of scientists that do meaningful work remains relatively constant over time, no matter how many scientists we add to the pool it seems to make very little difference. Just why this is true, we aren’t sure.