Sweet Angel...er...I mean Sweet Naïve Angel. There are NO discounts or upgrades on
DCL - even for returning cruisers.
Well there are actually a few.
1) DCL will sometimes give complementry upgrades - so far no real set of "criteria" has been identified on who, how or why they are given. My observation is that if you have a cat 11 gty room, you have the best chance of being upgraded.
2) Sometimes you are able to purchase a room upgrade at the port. Most of the time you are not able because the ship is "full"
3) Sometimes you can get a room credit if you book the cruise with the Disney VISA.
4) Most cruises that you book onboard will earn you a room credit - depending upon the length of cruise and if it's a special one or not and when the cruise is sailing.
5) Back to the Disney Visa - If you charge your vacation with it you can take 6 months to pay it off interest free. I haven't tried this yet (next year). Be sure to check with Bank One to see how this really works.
6) Like MMouse37 said - If you are a Florida resident and can be flexible as to when you can sail and how "short of a notice" you need to sail, you can get a good Florida discount. (I wonder if you gave DCL a Florida address and an out of state mailing address if they would notice?

)
7) Finally, you can find a
travel agent (like
Dreams Unlimited) that will give you discounts and/or room credits with your booking.
There may be other discounts/credit available - I'm just not remembering them at this time.