Personally, if this were mine, I'd be looking at making what I already have work even harder for me, but playing with the volume of each part a little more..adding automation to the various gain levels and causing more movement in that area..slowly morphing things about a little. Basically make this very much a track of solos and build things up to bring everything together at the end.
I'd start off with those found sounds you're talking about getting..or hopefully have got already by this time. Maybe a cityscape down low and bring the current start as it is and build from there.
The suggestion from BoJoProductions
about including some ethereal vocals is a good one, too. That said, I'd go easy on any if I were to use them..just a slight hint of vocals..even only an "Ah" or "Ouu" that repeats throughout..and even then I'd keep it very much in the background down low with reverb on it to help give it a feel of distance.
Looking forward to hearing where you do take this. Best of luck with it.