The headlight mod does helpat least some. As stated though, thats only if you have an open element filter. Then you get fresh, cool air in there.
Like Josh said, it's easy, free, and can't hurt.
Personally, I've raced plenty of times, and can show proof that its good for at least marginally. And on especially cool days, it helps a good bit
As for the spoiler. I am gonna kep mine on there. The function of a spoiler is to add a down force on the back of the car at higher speeds, helping the rear to not "float" at high speeds. And when you get to the end of the 1/4, IMO, those are pretty high speeds. Its not worth it IMO.
Also, I have a 2000, so I have the "cool" stock spoiler
-Will