What should I buy autograph-wise?

I collect autograhs and I have a Nelson cruz bat, mark texiera ball, Kenny Rogers photo, Josh Hamilton al MVP picture, Ian kindler jersey and a dirk jersey all signed....I thought about getting a Michael Jordan jersey but I'm afraid value will go down? What do you think I should get if I can find it? I buy mostly everything at field of dreams in Dallas..but I also met dirk so I kinda got lucky on that one