I wear dresses to the parks all of the time! Never had an issue on rides - though one time the edge of my dress got stuck in my underwear in the BOG bathroom - luckily another guest flagged me down before I left
I'm not too familiar with the roller coasters at Universal, but any that have your legs dangling might be an issue (like Soarin', but that's completely dark and has a ton of straps)
Second the body glide!! Even if you don't think you will need it, you will - I am pretty thin and never use it except for running in real life, but all of the time at Disney!