We were just starting to discuss this in the DIY coroplast grill block thread, and I decided to split it off to a new thread as its a separate topic.
Our cars have a pretty large hood gap IMO. It can't be good for aerodynamics, and it can't be good for fast warm up times. As I mentioned in my other thread, I have blocked off all of the grill area, but this is the one area that remains. Most other cars seem to have some form of gasket on the hood so it seals air off from the engine bay. However, our Mirages do not have this feature. They simply have a large gap that allows air to gush in or out at will.
Here is the underside of my 2014 DE Mirage. As you can see, its just metal.
In comparison, here is a 2004 Honda Civic under hood picture. They seem to have gasket around the headlights, and a small piece to the right of the hood latch.
In any case, I think it would be a good idea to close up this gap. It'll improve aerodynamics as well as speed up warm up times a little which is always welcome. It should also be pretty simple. A little bit of adhesive backed weather stripping should do the job I would imagine.
Other ideas and thoughts are very welcome. I am pretty sure that a few others have done this. If you guys could ante in, that would be great!