We cruised with Disney last year and had "heard" about the discounts to first time cruisers also. From what I found re-peat cruisers who sign up to recieve Disney liturature have access to post cards (through Disney mailings) that they can hand out to friends, family ect. for ship board credits to first time Disney Cruisers. However, they are hard to come by and some people have had conflicting results. Some are told they only need to call Disney with the correct code and some are told they have to mail in the postcard by the expiration date on the card. I signed up on a differant board to recieve one of these from a repeat cruiser, however I never did get the card or the code. It seems Disney is very secretive with their discount codes. We had a heck of a time getting the $200.00 discount I found on board through our TA. Until we said the magic words at the time it was "Sunshine Sailaway" and then poof ! $200.00 off. All I can say is research, research, research and don't expect your TA to know everything!
Good luck!
Tracy