THERE IS A LOT OF MYSTERY SURROUNDING FREE UPGRADES, where you pay for a lower category and somehow wind up with a higher room category than what you purchased originally. Although some cruise lines do offer seasonal upgrade specials, much of the commotion is unwarranted, and there is a lot of mythology traveling by word-of-mouth and the Internet.
Each cruise line has its own policies, ways and means of upgrading passengers, but the how’s and why’s are more closely guarded than some government secrets. It's all internal and can be based on past passenger status, the amount of money paid, when the booking was made, the credibility and relationship of the agency that booked your cruise, and sometimes it's a computer randomly pulling a name. Expecting your travel agent call every week to pester the cruise line for a free upgrade will more likely move you down the mystery list than up, as the cruise lines have ways of electronically flagging problem records, and that may enter into the secret upgrade equation.
Part of the mythology is that the cruise lines have lots of open staterooms each week that they give out to people. This perception is very far from the truth. Even with all the new and larger ships, 99% of the staterooms are sold out by the time the sailing date rolls around. Passengers, who think they can complain loudly to someone and get something for nothing, generally wind up just complaining loudly. No cruise line is going to move another paying passenger out of their stateroom to accommodate another wanting something for free. It’s basic and common sense.
Most cruise lines offer seasonal promotional specials where passengers are given the opportunity to purchase free upgrades at the time of booking. There are some promotions where you can get a 1 or 2 category upgrade at the time you confirm your reservation with a deposit, but with today's modern ships that really doesn't get you much. Let's look at the 2 largest cruise lines, Carnival and Royal Caribbean.
On Carnival Cruise Lines, if you purchase a minimum inside stateroom with twin beds, sometimes you can get upgraded, or you can pay for an upgrade to a higher category. In each case, the staterooms are 100% identical other than location. They are all exactly the same in every detail. Oceanview staterooms are all the same, and balcony staterooms are identical as well, until you get up into the suite categories. So with the cookie-cutter shipbuilding, an upgrade doesn't mean better accommodations, it means up a flight of stairs or two. For many people, this is not necessarily a good thing.
Royal Caribbean is very similar regarding stateroom upgrades. Inside categories are virtually identical staterooms. Outside staterooms are also identical, though on their older ships, some have picture windows, while others have portholes. But you get the idea. If you're thinking you can pay for the minimum inside, and when you arrive at the ship they will have you upgraded into a suite, it's probably just not true.
FROM OUR STANDPOINT, STATEROOM LOCATION IS MUCH MORE IMPORTANT THAN CATEGORY. If you can get an upgrade that gets you one deck closer to the activities deck, and still get a good location for free, then why not? But there is a lot more perception than reality when it comes to upgrading. You should always purchase a stateroom you'd be happy with regardless, and enjoy your cruise vacation.