So far we have only every had an inside room - this year we are going to the Panama Canal and have decided on a balcony - we loved the inside cabin - lovely for a pre dinner snooze nice and dark. We kept the TV on the webcam (little window on the world) so we could see when we were coming into port we were have been on the Sea Princess and the Sun Princess there is a little secret deck right at the front on Baja deck and we used to go there when we were coming into port. We hardly spent any time in the cabin. My advice is go for it you are still cruising!
As this is transatlantic in winter why not book a high grade inside and hope that the upgrade fairy is good to yo.
Try spending 14 days in your bedroom cupboard at home and see if you like inside rooms...!!! Personally I don't think any one could go from a balcony to an inside. Can't you split the difference and at least have a window.
We love our inside staterooms.We have had balcony and windows, and for the short time you are in your cabin its not worth the extra.If you like to go back to your cabin and want to stay there for a few hours, then perhaps a balcony would be best, also you wont be able to sit on the balcony in December going Translantic.
I totally agree with "aldrich". Even if you don't set foot on your balcony (but I can't believe you won't), the sense of space and the extra light a balcony gives you is worth the money.