Last minute upgrades are just PURE LUCK!!! I don't believe in the Upgrade Fairy like a lot of people do on this message board. Some people have met the Upgrade Fairy big time. But I haven't and there are others like me who haven't either.
I am in the habit of paying for an upgrade in advance because once you get on the ship you will see a BIG SIGN that says, "All cabins are filled". They say something like that.
My advise is to just be happy with what you have unless your intuition tells you to move to another cabin. Just call your travel agent and ask him/her to move you to a better location.
I once got an upgrade for just $35. more to a higher deck but it was offered to me by my travel agent through the cruise-line. I paid the money and was moved up to the Lido deck
near the Horizon Court Buffet. LOL.