I dont know what your intentions are with this tune, but I think its safe to say that youre going for minimalism
. I think that the lead gets a bit repetative after a while, and the obviuos advice would be to add some pads playing a very slow chord progression - c-f-g-d but more like he same chord but varying coloration (like Cm Add9 - Cm add7 and so on) that could evolve slowly, maybe filtered out totally and gradually opening the filter up during he entire tune, and maybe add a lead thats playing a melody and so on. But if we stick to the minimalism and dont add more layers/sounds, I would love to play around with automating the attack, sustain and decay of the lead you allready got. Like starting out with a slow attack that gradually speeds up - I imagine the effect would be like the sound is focusing and taking form - and then on the way towards the finale, maybe tweak the decay and sustain just a little bit here and there to create small variations in sound. And then for the grand finale I would slowly increase the sustain and release until the sound/melody is totally blurred and becomes more like a pad than a lead, and then decrease them both quickly so that the lead sound is back to its original state and the fade out the tune.
Sorry if Im taking over youre tune, I just got inspired by it, but I hope its an idea you can toy around with a little bit, and in the end its your tune and you know best what to do with it, if anything.