The weakening yen IS good for the profit of nintendo, but technically it reduces the price of the stock. This is what is happening to NTDOY. So only when the earnings come out and nintendo shows how much profit they made THANKS to the weakening yen, only then the stock will go beyond its technical value.
I am waiting to see how many wii u sales are sold globally last week to estimate the sales of wii u without the holiday season bias. 3ds is defiantly selling strong thanks to superb and unique software. I think that even if they won't make any profit from wii u we should trade around 20 a share. But I am sure they do make profit from wii u. You have to take in account their huge cash pile, and I think the last holiday season brought them even more cash from selling 3 major devices at one time. Now how much of cash depends on the yen now. I know that in the last earning all their estimates were made on assumption for 78 yen and not 87 like today.