It's actually not that much more -- it's a $30 difference between tower and tower MK in value season.
I had a conversation with a CM about this, and he said it looks as though there is not currently enough demand for tower MK to completely fill the MK side. In other words, even though the rooms on the 5th through 11th floors are roughly 50/50 MK views (actually closer to 45/55), they aren't selling 50 percent in the "tower MK" category, and are not blocking it that way. This is a little complicated, but what this means is that, suppose there are 280 bay side rooms at the contemporary. Once they have booked 280 "tower" rooms, they don't say they are sold out. They will continue to book and sell them as "tower" rooms (not "tower MK" rooms), but someone is going to end up getting an MK view. It is, however, considered and upgrade. So, to make a long story short, if you book at tower room and put a request in for MK, you still may get it, you're just not guaranteed and the chances are less than 50/50, depending on how many tower MK rooms they have sold.
They are apparently also tinkering with splitting up the tower club into MK and bay, so you could reserve a 12th floor room with guaranteed MK view. It would cost slightly more. Don't look for this real soon, though, because they made a big jump this year on the price of the tower club already, and to raise half of them another $30 might be a problem before people start staying there and seeing the renovations and the fact that it's not going to be concierge "light" any more. Still, don't be surprised to see a tower club MK show up in late 2007 or 2008.
Since there is currently no guaranteed MK in the tower club, if you book tower club and request MK, your chances are still pretty good of getting one, just not 100 percent.