If you like to take photos, early park admission is a great way to avoid the crowds. As you probably already know, only certain areas are open for EE; in the Studios, everyone seems to make a beeline to Diagon Alley. Thus, the queue for Harry Potter and the Escape from Gringotts. This queue times will only increase once the park opens to everyone, so EE is worth it if you want to try to ride more than once, or try out your wands at all the popular spell spots. I’ve also experienced a quick entry onto the Hogwarts Express to get into Hogsmeade once IOA opens — a great way to get to the back of that park quickly, if you don’t mind park hopping.
As I recall, the Mummy coaster is sometimes open during EE, or the Minions ride. You can likely find the list on Universal’s website.
If you enjoy doughnuts, I have rarely seen a line inside Voodoo when I arrive for EE. They have Halloween decorations up, including wooden caskets and some clever-looking mannequins on the spiral staircase. I have not stopped to properly admire their work, or try the special-edition HHN doughnuts yet.
If you want to eat breakfast in the park, EE is better for a meal at the Leaky Cauldron, I would guess. Easier to admire the theming without so many other guests crowding in.
