I was born in Portugual, so Portuguese and Spanish was all I heard growing up. But then I went into a german school and picked up German and English. Later I picked up French and finally Dutch.
My wife has a pretty similar language history so it's quite fun to speak our own version of Esperanto to our daughter and see what language she'll pick up first!
Workwise, I would be miles behind where I am right now if I hadn't picked up English at an early age. I've read somewhere that people who reason in a non-native language are able to maintain a more rational (less emotional) train of thought and that certainly seems to be the case with me, but if for no other reason, I suggest you should pick up a second language because it will increase your potential earnings! (see the economist's article below).
http://www.economist.com/blogs/prospero/2014/03/language-stu...