Lots of good reasons to have wifi at a baseball game. First is MLB At Bat. A great application with real-time statistics. Second is to pay attention to other sporting events (results). Third is social networking (Twitter someone about a great play). Fourth is to send photos to people from the event. Fifth is to follow a breaking news story. I could go on, but that's enough for now....
OK those are good reasons to have it, but none are really good for the Yankees to pay for it. That's what I was going for. Of course with baseball's "here are a million other things you can do aside from watch the darn game" approach, maybe someone will do that.