If 15% of 9th graders go on to become programmers, scientists, actuaries, etc (where maybe 40% (at best) of these use calc, probability, linear algebra, etc.),

If 15% of 9th graders go on to become programmers, scientists, actuaries, etc (where maybe 40% (at best) of these use calc, probability, linear algebra, etc.), then at least 85% of 9th graders are talking math that they will never use. Side note, the same could be said for Chemistry and Biology -- while interesting in the abstract maybe, the actual utility is minimal. I have never had to balance a stoichiometric equation nor do I expect to to see one any time soon. I would agree, as a guess, that learning "higher" math helps you think more clearly or in a more focused way for a longer period of time.