I agree that is the best solution.
What I did is to protect the open velocity stacks and jet access on the Webers from water.
If you look at the way the carbs were isolated in the original GT40's, there was a "cookie sheet" that isolated the stacks and in effect created an isolation chamber under the rear window.
Many presumed that was for "ram/cool air effect" but it may be more to your point of keeping the water out of them.
Those cars were often run very hard in very hard rain during races.
The "sugar scoop" changes the air flow in the car. It directs air down to a certain degree and up over the car as well.
It's an entirely different effect of putting a spoiler or a wing further back on the car.
Personally I don't think the sugar scoop design and location was entirely arbitrary and just cosmetic.
The formula as I recall is lift vs drag. If the number comes up as 1 or greater, you have flight.
With a wing, the design is averaged to where the downward force has the effect of putting down force on the rear suspension and the drag on the car as a result is minimal or minimalized as best can be done.
Downforce helps the entire car stick better and drag slows down the top speed of the car. Usually about 5mph somewhere around 195 to 200 mph.
A cookie sheet would probably be in order with Webers IF one was going to drive the car in the rain and leave ventilation through the factory provided areas in the engine bay.
I would suggest that BY FAR the simplest solution for YOU, all things considered, change the air cleaner assembly. MAYBE go back to the original FORD air cleaner?
All wings will create drag.
The only alternative to that I can think of is to add adjustable "ailerons" to the wing.