I've upgraded to a verandah once, and we've asked a few times. For Alaska we tried, but we couldn't get there early (we barely got there at all
) and they were out. For a Caribbean cruise we asked and were tempted by an upgrade to a one bedroom, but we didnt. Two other cruises we've asked and there were none available.
I'm definitely hoping to upgrade in September.
Kelly described it very well. If you look at what category you are assigned to now and what you would like to go to you can get a rough idea of price.
The upgrade price is determined by the difference in cost between those two categories. You will usually pay between 30%-50% of the price difference. There is often even a bigger discount for concierge.
I would never tell someone to book a category they won't be happy in, in the hopes that they can upgrade in the port because there are many many sailings where there is nothing available. But if you've got a little extra cash and want to try, do it!
You could score a great deal!