I am not aware of any. I have sailed several times and my TA (who knows I am a DVC member) has never mentioned a discount. She's usually pretty good about catching stuff like that.
I think the best way to leverage your DVC membership is to rent your points and put the cash toward your cruise fare. Booking with DCL directly through DVC is, from my understanding, not an efficient use of your points. I think John mentioned this on a podcast a long time ago, and I have heard that assertion made by many other podcasts since then. YMMV.
Nope. My guess is that they (inconsistently) offer the discount at the parks because you are likely using your DVC membership to stay on-property to visit said parks. Odds are much lower that you used your points to sail on DCL.
You can go to the members mixer to get some swag and free drinks, and entered to win OBC. Then stop by the DVC desk each day for your free swag. Lithographs are common one day.
We have gotten DVC discounts a couple of times on slow sailing cruises over the past five years. Usually a discount to go from a porthole room to a veranda.. One time we went from a 9C to 4B and also got some funds back,.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!