Parity in terms of season results is a lot higher in Baseball than it is in Football or Basketball.
In the last 10 years, there have been 8? different WS champs? The playoffs have been largely diverse as well.
IMO, baseball would improve more from a salary floor than a salary cap.
Also, a lot can happen in 5 years. In 5 years, the Yanks will be without Mo, Jeter, Granderson, Cano, Tex, A-Rod, Pettitte, probably Sabathia, Kuroda, probably Hughes...etc. In 5 years, based on prospects, every other team will surpass them unless they start trading some useless people (hello, Cano?) away.