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.
If all you have is a hammer, every problem begins to look like a nail.
There are times when having a screwdriver or pair of pliers makes a complicated problem trivial.
Nobody asks contractors, carpenters, etc, "Why learn to use a screwdriver if i already have a hammer?".  Really good contractors/carpenters have tons of tools and know how to use them well.  All programmers should be doing the same thing, learning to use new tools and use them well.

But before we use any power tools, lets
  take a moment to talk about shop safety.  Be sure
  to read, understand, and follow all the
  safety rules that come with your power
  tools.  Doing so will greatly reduce
  the risk of personal injury.  And remember
  this: there is no more important rule
  than to wear these: safety glasses
  -- Norm
Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?