Not a dumb idea to ask first.
Not a dumb idea to add an air dam.
It's hard to go on just a single picture of a typical 300d. What is the use case IOW where and how do you use it? Rally-cross much? Are you going to stance it?
It appears to have a vestigal air-dam already, so do you have mounting holes? Are you adverse to altering the bumper?
Rather than the conventional conveyor belt style, you could make a diamond-plate skid pan from the bumper to the front crossmember and put L-shaped scoops under the ends of the bumper so they form a converging duct with the front valance to energize the air striking the front tires. Sort of an anti-spat.
edit:
well, that's a lot of hand-waving.
I got this far and foundered on not wanting to drill holes in that shiny bumper.
That's an early bumper over-rider upside down under a later bumper. Here is some CAD (cardboard aided design)
I was intending to close the L-shape to the under-rider. You might notice the gap-filler at the back of the duct; the Superbeetle has a pronounced curve to the valance.