Sailed Ncl, celebrity, carnival, costa, and royal and there is definitely something to paying a bit more up front. Celebrity frequently has sales if your a bit flexible about when your going it can be quite competitive with the rest. Definitely not worth twice as much but if you can grab something for 25% higher and appreciate a friendly staff, fine dining, activities such as art class or speakers about history, etc, it's worth it.
At the minimum give it a try once.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp