Honus & Me
by Dan Gutman (1997)
A struggling bench warmer discovers the ability to travel through time by wishing on baseball cards, and wrestles with the desire to use his power to make a lot of money (therefore getting his parents back together) or to do good and the right thing. He does learn the importance of self-confidence, a solid stance at the plate, and speed on the basepaths.
As one with a closet full of baseball cards, none of (or all of) which will ever fetch 400k and allow me to retire to a life of leisure and reading, I cry every time I read one of these books and the valuable card gets torn or destroyed and fails to bring our hero the riches he deserves. I do enjoy the historically accurate portrayals of the players and their game, and there is a positive moral usually involved.