.These aren't baseball examples, but they are off the top of my head. Tiger Woods and Donovan McNAbb had "off seasons" after getting amrried, I believe Shaq did as well
Tiger Woods had wrist, knee and spine injuries during 2003 and 2004. Getting married to a hot chick had nothing to do with it.
I find that when a player returns from a few days off because his wife had a healthy baby, he usually performs well immediately afterwards. If the baby has health issues it may distract that player. (Marcus Giles 2006?)
As far as players in contract years go, I think there are 2 types of players. Some players are relaxed and play better when under contract while others need the $$$ to set a fire under their arse.