I replied earlier, but I've been thinking about this since then.
I just don't think bathing suits are really that comfortable. Am I alone in this? Especially a one piece. It's ok if you're at a pool and can jump in now and then. I generally wear the Lands End swim skirt and tank top, which in no way would ever be seen as anything other than a swim suit, IMHO. I would not want to wear that in the parks all day. Especially with a shirt and shorts over it. I haven't worn a one piece in years, but I remember them as being terribly uncomfortable, especially when using the facilities

I think it is different for men. My husband and son will occasionally wear solid color swim trunks on hot days, but they just look like shorts (they wear athletic shirts with them).
In the warmer months we will bring the kids' suits so they can play at the Casey Jr. splash area, but then change them right afterwards. But really. There is Splash Mountain in MK and Kali in AK. You're not going to be wet all day. We are packing athletic gear as a "Sweat Management Strategy" (TM Mr. Campbell

) But I wouldn't dress specifically for these 2 rides.