Sitting in a pot in constant rain did no favors to my hydrangea. I think the leaf spots are a fungus, Cercospora. It apparently won't kill it, so I see no need to
try any kind of sprays.
I pruned all of the affected leaves, which has the added benefit of improving the air circulation--a contributing factor to the condition. It fortunately isn't affecting the blooms in the slightest!
This page has descriptions of other hydrangea diseases: