I listened to a Freakanomics Episode on parenting a few years ago. Worth a listen (transcript available too)[0]. From what I remember, activities aren't much of a determinate of a child success so much as appropriate parental attention/affection. (This corresponds to what I've heard from exes who were in graduate lvl psych programs).

[0] http://freakonomics.com/2011/08/17/new-freakonomics-radio-po...