Humm what a fun question. I guess it depends on what you like!
If you have a park pass then I personally would head to Epcot, dh and I have done this once sans kids! If you have used a day on your park pass or have a UPH or AP this could work. We did all the stuff at WS that he and I like, esp the live entertainment, voices of liberty, off kilter etc., had a drink at the bar in R&C and other things that we wouldn't do with the kids. You could eat at any of the great rests at WS or leave after Illuminations and have a late dinner at the Boardwark, (espn, spoodles or the brewery) maybe even a stop at Jellyrolls?
Of course there is DTD and PI, lots of great places to eat and drink and dance but again PI requires a separate admission so you would have to account for that.
If you have fav rides you skipped due to the kiddos you could hit a park for a short time and then venture off for something else. Especially easy if you use WDW transportation.
Have fun deciding and hit the restaurant board for more great ideas on where to eat. Can you tell I wish I had this decision to make!!
TJ