Definitely not. Of course you also want to make sure you are learning different styles of languages. Learning both C# and Java will not expand your mind in any major way, but learning Java and Haskell will. 

Check out the Book ["Seven Languages in Seven Weeks"][1] which will walk you threw an intro to Ruby, IO, Scala, Erlang, Prolog, Clojure and Haskell. IF you enjoy languages you will love that book. 


  [1]: http://pragprog.com/book/btlang/seven-languages-in-seven-weeks