We usually always RD, even if we have FPP for popular rides, because then we can ride at least one of them twice (for example Soarin' - go straight there at RD then ride again later with FPP). I am the farthest thing from a morning person, but I have RDed and not RDed at Disney, and getting there early is worth it. However, we usually go to MK twice during the week and don't feel the need to RD both days. If I was going to be there for 4 days and going to a different park each day, I would RD every day.