When we went to Grad night at DL long long ago, the "romantic ride" was the Journey into the atom. It got so romantic that they shut it down at about 3 am, lest there be any romantic babies. That attraction is now Buzz, which doesn't have the same dark cachet.
I suggest closing down MK, and Epcot. In MK ride the mine train at closing and they let you go around a couple of times. Then linger in the shop at Splash mountain, tie your shoes a million times, then look around and you will be the only one there, the air will be sweet, the castle will be changing colors and they will be piping in music just for you and the street sweeper.
In Epcot linger after Illuminations, and lounge on the bridge by France, glory in the little twinkling lights and tell yourself "remember."