Ok, first, your math is highly against acceptable principles. You cannot add percentages together to get a total. Percentages are multipliers, and to get a total you need to have the other variables in place. Like, 50% of what? Since we are not there yet, we cannot answer.
Now, just looking at 2012 in context, the Yanks spent like 206 mil, with the threshold around 178. That is ~28 million over the threshold. At the 17% rate, the yanks would pay and extra 28*$170,000=4.7 million... now those same numbers using 50% would be 14 million... almost a $10 million difference... to put that in perspective... that is the money to pay a player in the range of hiroki kuroda range, just thrown away with nothing to show for it.
I am sure management has tossed a few numbers around and realized that getting under for 2014, resets as well all know, but before the next 5 year window is up, a few of the bigger contracts will also fall off the table (ARod, CC, Tex...etc) making it even easier to get below the threshold again.