You know your four year old best, of course, and know what you want to do as a family.
Thought I'd throw this in, though. Also, my son when he was four might have been different than most four year olds that go to Disney.
But his very favorite thing for the whole vacation was swimming in the swimming pool, riding the monorail around, and riding the boats over to Wilderness Lodge and Fort Wilderness and back. We kind of catered to that (as all the adults me, DH, my mom, and my dad had been to the theme parks what seems like a zillion times) and upped the resort time and lowered the theme park time. He liked the resort stuff and hanging out there more than the theme parks. lol // We stayed at the Contemporary on a high floor in the tower, and he thought it was the coolest hotel ever. // It's not a night time parade or spectacular fireworks display, but FYI we absolutely loved watching the Electric Water Pagent from our balcony at the Contemporary nightly. // It's a trip I look back at fondly, really relaxing and fun.
This sounds like our trips when our kids were young. We had been a lot so we catered to them. We actually only scheduled one park day for a 5 day trip. One day we would ride boats, another would be riding the monorail and visiting resorts, one at DTD and one for the pool. We watched fireworks in their pj's from different beaches.

