i wouldnt mess around with reducing the weight one the doors if your car is gonna be your daily-driver.
i think its heavy for a reason - to protect you from accidents - esp. if you get hit from the sides or the door area.
that's right, you don't want to mess with making the door out of carbon fiber, and taking out the side steel door beams unless you only drive the car on the track. But really weight's not the issue so much as the energy of impact they are designed to absorb since the doors are relatively light in a very light car.