OK, I may not be popular from saying this, but I don't think as many cases of reported food poisoning is really food poisoning.
I think sometimes your stomach gets upset or uneasy because you aren't used to the water there.
I think sometimes your stomach isn't used to all the rides, ups and downs, spinning around, and eventually it just feels yucky.
I think your stomach isn't used to drinking soda 2-3x a day, churros, popcorn and mickey bars and by nighttime, it is upset.
You are touching handles, railings, seatbelts and so many germ infested things that you could get a virus very easily. (plus 80% of people there got there by airplane--germ city) You don't wash your hands as often as you do at home.
Like most people, you aren't on a regular routine, so your bowels get 'irregular' and out of whack, and therefore your stomach feels yucky.
So most people that think they have food poisoning, for the most part probably only have one of the above.
Unless your whole family at the same thing and you are all vomitting 3 hours later, it probably isn't food poisoning.
That being said, on our last night we ate at Crystal Palace. I had an upset stomach that night, and felt nauseous all night. (but no vomitting). The rest of the 7 people in our party ate there and nobody else felt bad at all. So I would never jump to the assumption that it was food poisoning.
I would say this: stick to bottled water when possible, limit junk food (but still have fun--it is vacation!!), don't drink a ton of soda, wash your hands as much as possible, or use hand sanitizer, and listen to your body. It will tell you when to have a rest!
Have fun! The buffets are great! (and those places are soooo busy, the food doesn't have time to sit there for long periods of time!)