There are only 2 full service locations in Universal Studios, Finnegans and Lombards, and I would suggest making priority seating now if you know when you're going. As for Island's, they also have 2 full service locations: Mythos and Confisco (character breakfast). If you want to do the character breakfast, definitly call now to set up a p.s. As for City Walk, Emeril's is the only place that you'll need a reservation 6 months in advance.
If you know where you want to go, I'd suggest going ahead and making priority seating arrangements just for a nice piece of mind. Have fun!