I have tinted windows with film which cost me 20 bucks for all windows in my car except the front one. Its a Toyota Corolla 2004 and the darkness might be equal or a bit less than bush's cadillac.
It all depends where you live, the laws that allows you to have a certain darkness. Down here in Ecuador (South America) you need to get a permit to tint your windows, I don't have a permit but I tell cops I have $2.00 and that he could take it or take his time to take my film out.
It does help a lot if you tint your windows. Before I tinted my windows, I had problems looking at my screen. The only problem would be looking at your mirrors. I have to pull them down if I start wreckless driving.