So much wisdom from everyone-- thank you!!
Y'all have talked me into more supportive shoes. I'm going to wear my Converse (with an added arch support), so I can adjust support easily. They're retro enough, and even though it's a rounded toe, they sort-of lengthen my leg somehow. (All the laces, I guess.) One of the days will be shorter, and I'll wear Toms (also with added arch support), which I find to be incredibly comfortable.
And I'm waiting for them to arrive (which I know violates the only-wear-worn-in-shoes rule!), but I'll also bring Merrell Agave 2 Lavish sandals in Aluminum and maybe a pair of 'Me Too' ballet flats (recommended by YLF-ers in past threads). I'll wear them for a day or so before, though, so they'll be a BIT broken-in.
I'm going to overpack shoes and clothes, so I can see how I feel and adjust last minute. If after the first day, I decide I want to do the exercise pants and regular sneakers, well that's what I'll do. (At least it will be 'cute' gear.) I think I'll even bring an extra pair of shoes to the park in my day pack each day, just in case. Of course I'll have Glide, too.
As for outfits, one day will be BF jeans (Lucky brand, medium color), a gray J Crew t-shirt that has some print around the neck and a shirttail hem (it's actually nice; I'm bad at describing clothes), and gray Converse. The other full-day-of-park will be either a navy blue ON dress with a scarf (the dress is VERY casual) and either Toms or Merrell sandals, OR KUT BF jeans with a TBD blouse and Toms or sandals. I can't wear dresses in the heat without Jockeys Skimmies, which are the best thing in the world (buy them if you ever have had 'chub rub'- they're heaven and you don't worry about flashing anyone).
We're not doing anything super fancy at night, so I'll probably wear white Kut jeans with a darker tank top on the nicer day, and other jeans with a top the other day. I'm rarely cold, but I'll bring something just in case.
I will report back with what I wear, and how it goes. I realize that I regularly search the archives, so even if no one on this thread cares about the outcome, it may help future YLFers going to Disney.
Thanks, y'all!