After years in the lighting industry, I would have to say that most US model headlights are 'over-designed' for safety of the other motorists and not the driver.
In reference to your wanting to use higher wattage lamps, it will not do much good.... A 500W lamp in a crappy reflector and crappy lens will give 500W of crappy light.
My best advise is to switch to the Euro system. The reflectors are truer parabolics and cleaner reflective surfaces. The lenses are designed more for concentrating the beams and not diffusing it like the US models. Follow Larry's advise and do it right, otherwise you will not be happy with them.
In the meantime, you can install an aux pair of HELLA 55W Driving lights. This will help out for now, and certianly will not hurt you when you install the Euro's.
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles