Is it desirable to build an application specific set of intermediate classes?

In working in VFP, I have a set of base classes, and for each application, I subclass the base classes. This allows changes in class behavior without writing over the base classes.

While working with MM .Net framework, it appears to me that the application forms are built directly from the MM base classes. This may be for clarity in the examples, but in real life, should I subclass the MM classes into application specific subclasses?

If yes, is there a tool or wizard that will do this form me?

Thanks
Don Lowrey