Till "collapsable object groups" get implemented.
You could make use of the layers to go easyer along with your objects. With respect to the Z-orders ofcourse.
The layer TAB on the right has a dropdown menu in the middle to filter out objects based on there layers.
You can also make Layers invisible/visible to aid.
You can select objects from the listed objects in the LAyers TAB.
You can drag layers to change Z-order easy.
You even can drag objects selected (in the low part) in the layer pane to differend layers (in the higher parts)