Back to the original question, it is very unlikely you will be offered an upgrade if you took an assigned cabin number. upgrades typically happen to those that book Cat Guarantee or "Run of the Ship". Essentially, you are guranteed to do no worse that the category you booked in. You may be moved anywhere on the ship as long as you don't drop in category. The cat guarantees, in my experience, typically put you aft or stern, as these are less desireable rooms due to they get more rocking motion.