At Restaurant Marrakesh, we were not able to order either of the two large "feasts" that are priced per person and served family style - I don't remember the names. They did let us "upgrade" the side dish on our entrees to couscous for free. Also, our waiter told us at first that we were limited to only the Baklava for dessert, but when it came time to order, he let us order anything we wanted (I had the Baklava anyway, my wife had the Crepes Atlas).
Interestingly, at O'Hana, our server mentioned (without us asking) that we could order a specialty drink (non-alcoholic) _in addition to_ the Coke/Tea/etc. on the Dining Plan. I don't think this is usual at most places, and I'm not sure if it was an exception or the rule at O'Hana.