Opening the hood scoops is personal preference. If you drive in the rain at all you will notice that the leading edge of the hood get's a little wet but from there back the rain will blow over the hood not on it. No water will get into the openings. Even while at a stop, very little water will go in through the openings and the air cleaner lid and intake manifold is about all that will get a few drips on them. (Usually when you open the hood to check is all)

I think Bjorn might have meant the second gen Formula hood scoops that were moved forward much like the 69 T/A. But the Cowl area is by far the best source for cool air with more neutral pressure...

But, the true RA cars draw in the cooler outside air by having the air intake sealed off to under hood air etc...

I've had two birds now with the open scoop... again, personal preference.

Brett!