This is such a hard question. We've done just Disney, Just Universal, and WDW & Universal trips (from Wisconsin). The two parks in one trip save airfare, but felt a park had to get the short end, or no resting time. Ticket prices get cheaper by the day the longer you pick (or annual pass). I feel a day per park with express pass is cutting close to not worth the per day price and heartbreak of missing a bunch of stuff because you don't have more time to re-configure due to weather, fatigue, ride issues. That being said, people have different sized pocketbooks and expectations. Just let your grandson know if things are missed this trip, it could be a future trip (if true--40+ years later I haven't let my parents forget their WDW promises).