Research has shown that simply cleaning the headlight lens will increase the lumens/ft on the average vehicle by 10%. It also drastically reduces the light scattering which is a nice thing for oncoming vehicles.
IMO, keep the headlights clean, then if you want more, consider bulbs up to the legal limit (55w IIRC, for low beams), consider a temperature (color) change if you want...but really you should avoid anything over 55w. One, it is not legal, two it is dangerous for oncoming traffic (particularly if your lenses are dirty or lights not adjusted properly), and three your wiring harness is not designed to hold that much current (which is why companies offer the harness upgrades).
If you still want more light, add some driving lights. This way you can turn them off when there is oncoming traffic. Some people find it amusing to blind people in other vehicles with uber-bright headlights, but it is a dangerous situation that can easily lead to someone being killed in an accident. Seriously, not worth it.
Driving lights will give you much more usable light than simply putting in higher wattage bulbs anyway, so if you are after light, don't goof around with high wattage replacement bulbs for your headlights. Install the appropriate auxillary lighting, and light up your path properly. The results will be better (more light), and the rest of the people on the road will still be able to see.
:ylsmoke: