The Smalltalk jewels are here.
This is the place to get source code and support for ValueInterface, the complete VisualWorks application framework in a can. ValueInterface can do more for you if your objects use the new extended change/update protocol. Your code will be even simpler if you use void, which is just like nil, except that it accepts any message, does nothing, and quietly returns self.
You might also want to look at LearningWorks, which is a full implementation of ParcPlace Smalltalk in a special learning environment that you can download for free!