>not a hard cap, again, use a "Bird Rule," because the Yankees never should have lost Derek Jeter because they were up against the cap
Well, with a hard cap, the Yankees wouldn't have faced that decision, either some of those years if they didn't want it - they just would have not been able to add as much additional salary as they did from other teams via free agency or trade as the seasons ebbed and flowed (i.e., Sabathia, Clemens, Giambi, Matsui, Mussina, ARod, Randy Johnson, Damon, etc).
I would add that a hard cap would also include full broadcast revenue sharing - meaning that the financial playing field, while not totally equal due to markets sizes, would be much more level and allow for all ballclubs to retain their homegrown stars longterm if they want them, in addition to shelling out money in free agency much more consistently. Huge market clubs still would have built in advantages if they are well run (similar to how many big market clubs were routinely playing for titles before MLB adopted free agency) - but the game would be much healthier and generate much more fan interest if the whole league had reasonable windows where their local team could win it all or could sign a marquee free agent from time to time. The NBA has a better financial model going than MLB along with more varaibility on who's playing for NBA titles from each conference, which is a black eye on MLB.