I'm a Florida resident and Premium Annual Passport holder... go lots of times and no problem for me so far... I'm not saying it's not possible and down right irritating if they show up, but they are not common. I work outside in Miami, and there are lots.of neighborhoods on the coast near mangrove swamps where they are so thick you can ALMOST see them!!!!!!!!!! Most often a problem when the sun doesn't shine and the wind doesn't blow(morning, evening, night)...
Anyone being bitten just on the legs is not being attacked by noseeums, even if they didn't see what bit them.
Lots of critters out there want your blood, never had them spoil a good time for me yet a WDW... been there too many times for it to be just luck... not saying you won't get bit, it's just not likely to be a PROBLEM... do be careful on the highway please.