Go - you will have a great time and seeing it through his eyes will make you so happy. We brought our dd last May at age 3. She loved it. She is tiny so she could not go on a lot of the bigger rides, but there is plenty for the little ones. I thought she would be afraid of the characters, so dh held her the first couple of times. Well after the 1st couple, she was running up to them and hugging them with so much joy and excitement. She loved the pool. When we arrived at the hotel and walked into the room,she said Ooooohhhhh!. Too funny.
She still talks about "the vacation" as she calls it. We are going again in October when she will have just turned 4 and she can't wait.
Bring a stroller (or rent one). Even if you end up pushing it around empty, you will have it if you need it. They get tired in the heat and excitement. Follow and go at your ds's pace. We had planned to do the early park, afternoon break routine. But dd was so tired at the end of the day, that we found it better to let her sleep a little later, have a slow morning eating breakfast and relaxing, and then going to the parks a bit later. You might want to plan a day in the middle of the week away from the parks at the pool.