I took mine when my youngest was just turning 2. We had a good time. I would suggest you stay at one of the onsite hotels and take advantage of FOTL. That way you could even take turns going to the parks and hanging out at the pool with the baby. They do an excellent job with the baby swap, but I would only do it with the FOTL with kids that little. Heck, that is the only way I would do it at all. Your son will probably think it is great to ride everything twice. I guess they thought about how much the parents enjoy watching their kids during the rides. My two year old was even tall enough to ride that kid roller coasters and enjoy the rides in Seuss Land and a lot of the attractions at Universal that don't have height requirements. These parks are SO aimed at 4 year old boys with the dinosaurs and aliens and flying cars and Spiderman and Jimmy Neutron and Shrek, the Animal Planet show, ET. All the things little boys (and the big boys) seem to love. I think your older son will get so much out of this. They will LOVE the pools and riding the boats to get to the parks. My sons are 6 and 4 now and we are going there for our 3rd or 4th visit. I can't keep track. Your one year old will love all the sights. And the Barney Show that we may get to skip this year! Take swim diapers with you, because there are a lot of little spash areas and water playgrounds to play in.
That being said, things will probably be easier the next October and your youngest would enjoy the parks too. If the three of you want to go this year, I would do it, it would not be that bad. If not, I would wait a year.