I think dresses are great in Disney! They're just one piece, so they're pretty easy to manage. I don't think they're a hassle at all. Plus, they are cool and light for the hot days in summer.
It depends on the dresses. I love wearing short dresses with shorts underneath and taking my crossbody bag. It wasn't bad when I did it since they were short dresses, and I didn't risk any flashes because of my shorts. I wouldn't wear long dresses though, like maxis. But I think short ones are fine.
My sister usually wears a dress about every day and is fine with it! Plan accordingly though because you probably wouldn't want a dress on a water ride, the carousel, Space Mountain, Tower of Terror, etc.