Quagga
Former Dictator
I don't think the wonder would be worth building just for Free Religion.
10% research bonus in all cities is worth something to me. Especially, if you're trying to avoid adopting a religion, it's better than Paganism. Besides, we don't know if the wonder would cost the same as Stonehenge or the same as Space Elevator.
Although I understand your point, it seems similar to saying that the Pyramids aren't worth building just to get Representation.
Anyway, it was just an idea of what to do with one of the multiple religious wonders that are coming with BtS.