Well, reading only your question "Name of the concept of designing an interface to allow expert users to become more efficient?" I'm inclined to point you toward The Humane Interface: New Directions for Designing Interactive Systems by Jef Raskin, in which there is the concept of habituation:
2-3-1 Formation of Habits
When you perform a task repeatedly, it
tends to become easier to do.
Juggling, table tennis, and playing
piano are everyday examples in my
life; they all seemed impossible when
I first attempted them. Walking is a
more widely practiced example. With
repetition, or practice, your
competence becomes habitual, and you
can do the task without having to
think about it. ...
...
... The ideal humane interface would
reduce the interface component of a
user's work to benign habituation.
Many of the problems that make
products difficult and unpleasant to
use are caused by human-machine design
that fails to take into account the
helpful and injurious properties of
habit formation. One notable example
is the tendency to provide many ways
of accomplishing the same task. Having
multiple options can shift your locus
of attention from the task to the
choice of method...
But is contrary to what you describe in your question, as evidenced by the last 2 sentences. In fact in that book there is also a sub-chapter dedicated to dispel the myth of beginner-expert dichotomy:
3-6 Myth of the Beginner-Expert Dichotomy
... This dichotomy is invalid. As a user
of a complex system, you are neither
a beginner nor an expert, and you cannot
be placed on a single continuum between
these two poles. You independently know
or do not know each feature or each related
set of features that work similarly to one
another. You may know how to use many
commands and features of a software package;
you may even work with the package professionally,
and people may seek your advice on using it.
Yet you may not know how to use or even know
about the existence of certain other commands
or even whole categories of commands in that
same package. ...
So, perhaps is not such a good term/concept that you are looking for.
Update: were you looking for the term Adaptive User Interfaces, perhaps? Well, I think that, as usually understood and implemented, it is not such a great idea (for example, disappearing menu items in Microsoft products). But my impression is that researchers use the term for something quite different.
Update: but Adaptive User Interfaces does not cover scripting.