Using higher power bulbs or HID in the stock housing will doing nothing more than create more glare for the opposing traffic and yourself. Additionally, HID in non HID housings is now illegal in the US.
The plain fact is that the oem US plastic headlamp housings put out crappy light because they conform to the crappy US lighting regulations. Add to this that most of them use 9006 or 9007 bulbs, which both rate near the bottom as far as lumens are concened.
What you can do is to add a set of really good aftermarket driving lamps in place of or addition to the oem "fog" lamps. Some of the cheap units found at Walmarts and what-not are better than oem, and there are much better units beyond that. For the best improvement, seek out lamps that have sharp upper and lower cutoffs and use parabolic lenses. These will throw most of the light down the road where you need it, and will waste little on the ground right in front of the vehicle, or up in the sky in driver's eyes.
Another option would be to install the best driving lamps on your vehicle. They don't have to be installed in place of the oem lamps, but you can do so if you like to work with fiberglass
The are made by Hella and can be found for about $50 each here:
http://www.rallylights.com/hella/90mm_modules.asp
Now, you may not be getting full voltage to your bulbs due to corrosion at connectors in the wiring, so you may want to look into replacing the wiring with a relay kit. My 95 SHO was dropping 1.2V to the wiring last fall. While this is only 8% of system voltage, I was in fact was losing about 20% of total lamp output due to this voltage loss. Installing a wire relay kit I cobbled together brought to voltage loss to just .03V, and the lamps put out considerably more light. Unfortunately, my vision did not get better as they were still junky US lamps. There was more light, but the glare increased as well. That's when I decided to scrap the whole thing for the Hella's.