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.
Im not sure if this is what you are looking for, but we write our main application with Java at the small company I work for, but have used python to write smaller scripts quickly.  Backup software, temporary scripts to manipulate data and push out results.  It just seems easier sometimes to sit down with python and write a quick script than mess with classes and stuff in java.  
Temp scripts that aren't going to stick around don't need a lot of design time wasted on them.
And I am lazy, but it is good to just learn as much as you can of course and see what features exist in other languages.  Knowing more never hurts you in future career changes :)
Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?