Air flows pretty well at the speed the engine fan gives it. I doubt the panel chokes the air flow. What is the fan speed? 2xengine rpm?
Race cars don't have it so you can access things quickly and see what's going on? Also, they have power to spare, who cares about a bit more wind resistance on the road track?
I decided to keep mine on. The reason is: Have you ever seen an engine of a car that went off in a gravel area of the track (or a road)? Have you seen what happens if gravel spray's the engine at 100mph? Not pretty.
My final remark is that I believe the effect of this panel is overrated - both ways. I believe that it does not make much of a difference in any effect, except for keeping stuff from hitting your engine.
George