The kid who can't make change was not a music student. He may have been 'musically stimulated' as you put it, but if he took music classes he can count (and subdivide) while playing an instrument at the same time.

The only example I see comparable (to me) above may be scouting, as it does involve a wide range of discipline, but I do not know of any peer reviewed studies showing it increases ones learning. With music there are many.

Quick refernce, but you can Google many -
http://www.ptcmusic.org/The_Stage_Academy_of_Music/The_Benefits_of_Music.html



Make your sound your own!
.. I do not work here, but the benefits are still awesome