There's a collected property for each VM on the power state. Why not use a heat map per folder to show this status where green equals on and red equals off?
I actually ended up taking an existing view in vROps - "Virtual Machines Power State Distribution" and using this in a view widget on the dashboard for a new group created based on the vCenter folder membership.
The complexity came with the crazy folder structure in the inventory and duplicated names in multiple vCenter's but the end result delivered the requirements. vSphere tags might be the answer for this one to be more simplistic.
Thanks for the response though!