I've had both and the Plaza Inn is the one that is my new "must do" on future trips! I loved every bit of the meal and it would have been even better if I'd remembered to ask for white meat only. The Carnation Cafe was a good meal, too, and we even got seated in the little gazebo on the patio for perfect people watching! My husband had the sourdough melt thing and thought it was ok but a little greasy, and there wasnt much else on the menu he was interested in. He loved the pot roast at the Plaza Inn! I would like to do Carnation Cafe for a breakfast with their large Mickey waffle, yum! I think it would be best to do both, like you said! And now just thinking about it makes me want to check the menu again and plot possibilities!
Have fun planning!