We did. We did buy an extra drink and on one occasion, an extra dessert (couldn't agree on the same one, LOL). We also tipped more than usual to make up for the server's extra trouble.
Enjoy your trip!
P.S. My DH and I share a lot of meals at Disney restaurants because the portions are so large. For us, it's the only way to enjoy an appetizer, entree and dessert at the same meal without stuffing ourselves. We have not encountered any problems doing so, and of course, we don't do it at the buffets, LOL!