We left there with time left over to go down to the waterside and the quay and see Vivid Sydney before they shut it off for the night. The interactive displays in the park weren't very interactive - we think they might have worked on shadows, so not much fun in the dark.
We had fun with a tree full of artificial fireflies which was a model of social interaction or some such - basically the lights responded to other lights, so the ones clumped together were very active, and the ones all alone at the far side of the tree were sad. I got a bit too attached to the sad fireflies and spent quite some time with the installed torches trying to make them feel like they had more friends.
The light show on the sails of the opera house was pretty, as was the one on Customs House, but the best thing by far was the Fire Dance in Campbell's Cove. As K says, humans are simple creatures. FIRE! IN WINTER! With music! We missed the first half of Firework - I think I want to go back and see the whole thing.
So there you go - I do get out of my cave sometimes.