Real Crocs are great for WDW. You can walk in them all day and your feet don't get tired or hot, plus there's no joint pain like there is with other shoes, even more expensive ones. Definitely splurge for the real Crocs. They are only $30, which is half the price of Merrels, Keens and Tevas, at least the styles I like.
Make sure you wear your Crocs for a few days before your trip. Your feet will be sweaty the first couple of times you wear them, but that will go away. And your feet don't smell when you don't wear socks.
The Prima style of Croc is much dressier, though it doesn't feel like it has as much arch support.