I think that depends on your weather. Here in Phoenix summer can get to 115* + so the very first thing I ever did to my car, before I was even in to modifying, was tint the windows. It is a huge difference between tinted windows and non tinted when you get into your car after it sits in the sun.
If you are doing it mostly for looks, then go with the lip. I personally believe if its useful, go with it.