<p>Should I be writing Doc Comments for all of my java methods? </p>

I
thoroughly
document every public method in every API class.  Classes which have public members but which are not intended for external consumption are prominently marked in the class javadoc.  I also document every protected method in every API class, though to a lesser extent.  This goes on the idea that any developer who is extending an API class will already have a fair concept of what's going on.
Finally, I will occasionally document private and package private methods for my own benefit.  Any method or field that I think needs some explanation in its usage will receive documentation, regardless of its visibility.