Nice effect, like it. I don't have a solution to the problem but I'll just throw my 2 pence in.
Bit of a long shot: You say your reusing your planes, which sounds great idea. But the fact that something is holding onto the Vector<Number> instances, perhaps away3d or (tweenMax) is storing the X,Y,Z & rotation properties for each tween. Maybe you could try not reusing but creating / destroying a plane each time to see if these properties are disassociated. However even if you fix this memory leek, there will be others. 8 hours is a long time to run a flash app, maybe you could write a script to close the programme and re-open it every 30 minutes?
