Accuracy is a useless stat for PT tanks (imo) as it only effects 3 abilities, only two of which generate heat, and only one of which you will actually use often. (Rail Shot) With 1.3 linking some of our AE threat to Rail Shot, it has become more important, but I still wouldn't bother with Accuracy.
Wanted to clarify on this further for you. With the AE threat to Rail shot, etc, it is only based off the initial hit. If you miss Rail shot on your initial target, Ion isn't spread. However if you hit, there are no accuracy checks for Ion on each individual mob thereafter. It applies a blanket so to speak.
As said above, Accuracy is useless. From a spec standpoint, I even took out the 2 points in Iron Fist for endurance. Since they nerfed our DPS anyway as it is not needed for threat, I wanted to see how much of a difference it really was. In the end, not much difference in dmg comparing same fights from 1.2/1.3.