It looks like your ventilation is already pretty good with one whole wall being open inside. As for doing it for the sake of headspace, I would just be worried about doing much with that wood. If it's similar to what my prefab is made of, even putting a single screw through it has made it...
I covered all the wire walls on my prefab (similar to yours) with plywood and left room for ventilation, so the entire structure became the whole coop. I kept the floor dirt. I also added an extra roost inside the dirt floor area. Let me know if you want pictures, because I can get some at some...