It is a good thing to diversify.
(t) I learned Erlang and Lisp and literally carved out a part of Powerset that had a problem to solve. Now my Erlang code is part of bing.com, and our startup got bought and integrated into Microsoft.com.
(t - 1) I decided to learn Ruby, and started to do a bit of open source work with it. It managed to get me out of a dead end career grind at Lockheed Martin by catching the eye of a silicon valley recruiter.
(t - 2) I decided to learn Lisp, which allowed me to meet a lot of talented developers and work on some really interesting projects, and network with climate scientists who were working in conjunction with me as part of Lockheed Martin RSAII project doing data modeling. This helped me land a job at Lockheed during the worst parts of the post-bubble recession, elevating me from hand-to-mouth temp work (you sure do type fast, sir!) to software engineering.