I seem to recall reading somewhere that intelligence and work ethic affect player development, but I don't recall how they do or where I read it. Helpful, eh?
edit: Aha! From pp.258-259 of the game guide:
"Intelligent players may have some positive effect on other players in the clubhouse, and can influence in-game decisions and player development.... Players with a strong work ethic may have some positive effect on other players in the clubhouse, and can influence player development, slump management, etc."