Since my kids are 3.5 and short, DH and I would use a date night to ride things we can't because of the kids. We would probably eat at Columbia Harbor House and then ride Mine Train, Splash Mountain and Big Thunder. Or we would do a progressive dinner through World Showcase, drinks in Mexico, dinner from somewhere, dessert in France, then watch Illuminations.
If you want to do a sit-down, we love some of the signature restaurants at the resorts. Victoria and Alberts if it's in the budget, Artist Point at the Wilderness Lodge, Flying Fish at the Boardwalk, Sanaa or Jiko at the Animal Kingdom Lodge.
Another thing we've done that was amazing was the afternoon tea at the Grand Floridian. I know it's not a "night" thing, but we did it at 4:00 and then were too full for a real dinner. So we walked around Magic Kingdom then had a treat from the Main Street Bakery.