Pixar you won't need the dining option..plenty of seats without arriving far ahead of showtime.
RoL, yea I'd only do the dining option if I already planned on eating at Tiffins or Tusker. If I wasn't already planning to eat at one, I wouldn't shell out the money just to do the dining plan.
If you'd like to see RoL badly, I'd show up 60 or more minutes to get a seat. If you'd like to see RoL but wouldn't be disappointed if it was already at capacity, then I'd recommend showing up 30 min or so ahead of showtime. As long as you can get a seat, there's really no bad seats in the arena.