I think we should be content in that which the Lord has provided for us. Contentment is simply a lack of dissatisfaction. That's not to say that you can't dream or have ambition...so long as those hopes and ambitions are not contrary to our purpose as the witnesses of Christ. If your dreams or ambitions require you to do anything that is not loving towards your neighbors, then perhaps those dreams and ambitions are not what God has in store for you.
It's funny, because I am on several dating websites, and a lot of the women's profiles make it point that they want a man with goals, someone with ambition. It just makes me laugh; I have no corporate ladder to climb. I like teaching music, and my only goal is to do it better. I can dream of a perfect world where every student I have practices every single day, and follows every instruction I give them, and we go to contest and get First Divisions every time. Man, that'd be great. Oh, and if I were married to Allison Brie or Kari Jobe or something, that'd be awesome, too.
But ya know, my students, for the most part, are pretty good. They try hard. I could teach better. They aren't disrepectful. No one has keyed my car yet (knock wood). I haven't been sued by an angry parent (knock wood). In a time when arts positions are being cut, my principal is defending my position and fighting for me. I receive sufficient compensation that pays for a roof over my head, lots of food, and I have a loving family and a loving church family. How could I not be content?
God provides. Be content. Want more, so long as you can be happy with what He's already given.