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"Seven Languages in Seven Weeks, which will walk you threwthrough an intro to Ruby, IO, Scala, Erlang, Prolog, Clojure and Haskell. IF you enjoy languages you will love that book.