I read yesterday that you want to close the vents to keep water out, which sounds fine BUT won't the water just pool up behind the vents where it is closed? The vents are depressed into the hood correct? so there is a depression in the hood where the vents have been added. That is my thought on that. I would suggest some sort of gutter to channel that water off to the sides of the engine bay instead of closing them. A friend of mine had a hood like this and I asked him about rain and water, he seemed happy to let his engine get wet.
One more thing, don't forget the Z has the undertray so water can pool up there too.