I packed a suit to wear at the two formal dinners, and another jacket to wear at Palo or Lumière's. I packed a few different shirts and ties to make the jacket and suit go a little further.
Depending on your dining rotation and when (or if) you eat at Palo, you'll need the suit for dinner on Sunday and Thursday (formal nights), a jacket for Lumière's on the non-themed night you eat there, and a jacket for Palo. I'd definitely make the jacket do double-duty for both Palo and Lumière's.
On one cruise, we did Palo on the same night as the Lumière's night, so I really only needed the jacket once. Of course, that was my first cruise, and I packed the suit and two jackets, which was indeed overkill...