I think hood vents are usually done along with fender vents... I think hood vents will give even less gains than fender vents but I guess a gain is a gain...
hood vents can be tricky because you need the vent to be in an area of airflow that creates a negative pressure in airflow for it to extract air, otherwise it'd either be stagnant, or even worse it could act as a scoop & do nothing to help... hood vents are usually done in the center of the hood or slightly foward of that, too far back & the pressure buildup at the base of the windshield will not let it be as effective...
one old hot rodder trick we used to do was remove the rear weatherstrip seal to the hood, allowing airflow through the back of the hood, although the turbulence in this area is high it still does help extract some air... the reason the factory seals this area well though is so if you had a radiator hose blow or something you wouldn't have a windshield covered with antifreeze, or worse even oil... but this is a small performance enhancement that can be done & aside from the danger of underhood fluids winding up on the windshield, it's a good thing to do... I used to always do this, haven't on the fx though...
