A big thumbs up to Spring Training. Being from CA, of course, the Dodgers right in Vero would be a big draw. The Mets are also a short drive away in Port St. Lucie --- they have a great stadium. Games at Disney have all the special Disney touches you might expect. Last year (first Spring Training trip) we got to see the Braves play LA and Tommy Lasorda was in the stands. He was a great guy -- he let the ushers bring people (mostly children) to him throughout the game and he chatted with all of them and signed some autographs.
Early January is when the schedules come out. The Yankee games at WDW tend to sell out pretty quickly and you really need to buy them the day they start sales. Other games are also brisk sells but not as crucial to be on the mark.