I would ask what it would cost to get the unobstructed view (or mostly so). The port hole is not that great. The oceanview rooms are mostly the same sq footage so its the view you pay extra for.
I'm not that big on having to have a view. MOST of the time I am up on deck somewhere and don't care that I can't see anything but a life boat out of my window. I just use it for the light. If you plan on sitting in your cabin and staring out the window at the water... you are best off going to a balcony cabin.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007