I already explained why Jeter should move to third: because he cares about winning, and that will give the Yankees the best chance at winning. It's been a few years.
The owners would love to have a salary cap, and tried very hard to get one. In fact, they implemented a cap when they declared an impasse in the negotiations, but it was overturned by the 2nd Circuit Court of Appeals. I don't think the union will ever go for a cap. Even if they had a cap now, it would probably only affect the Yankees. Even so, the union loves having the Yankees there so they can drive up the salaries for everyone.
Oh, and I'll be shocked if Boone's contract gets voided.