My DH and I just went in May for a late anniversary trip. It was FABULOUS!!! We did things together that 1) we would never be able to afford for our whole family; 2) we would (personally) never bring our kids with us to do; and 3) would never be accomplished with our kids! Some examples are that we actually stayed on property - with a family of 6, staying on property is just not a financially feasible option for us. We were able to have a very nice dinner at Jiko (highly recommend, would never do with our kids). We loved *leisurely* touring Epcot World Showcase, and were there from OPEN to CLOSE, which would be difficult to do with our kids, or at least do without lots of complaining. We also did the Wishes Dessert Party together. The desserts are good, but more importantly, it was so relaxing to be able to enjoy the fireworks without the crowds!
But THE very best thing was being able to do what WE wanted to do WHEN we wanted to do it. I just asked my DH what he liked best about our trip to Disney, and he said "Going to Disney with NO KIDS!" And, unlike PPs, did I miss our kids? NOPE!! I love my kids dearly, but I loved getting to spend time alone with my DH at such a fun place! I hope we get to do it again sometime, because there are so many other things there we'd love to do together.
So, if you are both fans of WDW, I think you will find plenty of fun things to do together as adults.