I would not recommend header wrap for people who live in snowy winter climates, or rainy humid climates. The do block heat, but they trap moisture underneath them and that leads to massive rusting. Especialy if they salt the roads when it snows. The trapped salt wear carode the headers in no time. Ceramic coatings help the header retain heat a bit, but it won´t cool your underhood temps that drasticly. They do however extend the life of your header, and make it look a lot nicer. The only thing that heat really affects under the hood is the intake air temp anyway, so if you can relocate your air filter to a cooler place then your set.
I would not attempt to redirect the air flow.The air coming up from under the car would cool the header somewhat but it would also slow the air coming through the radiator decreasing the effectiveness of your cooling system.