I wonder why would a C++, C#, Java developer want to learn a dynamic language?
Assuming the company won't switch its main development language from C++/C#/Java to a dynamic one what use is there for a dynamic language?
What helper tasks can be done by the dynamic languages faster or better after only a few days of learning than with the static language that you have been using for several years?
Update
After seeing the first few responses it is clear that there are two issues.
My main interest would be something that is justifiable to the employer as an expense.
That is, I am looking for justifications for the employer to finance the learning of a dynamic language. Aside from the obvious that the employee will have broader view, the
employers are usually looking for some "real" benefit.
Learning something with a flexible OOP system, like Lisp or Perl (see Moose), will allow you to better expand and understand your thoughts on software engineering.  Ideally, every language has some unique facet (whether it be CLOS or some other technique) that enhances, extends and grows your abilities as a programmer.
Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?