Perhaps the best bang-for-the-buck headlight upgrade is to replace the stock fluted headlamp with an non-fluted E-code (European) light. Add an 80/100w bulb and you've got a major improvement in visibility for about $50.
I have the Hella E-code headlights with Hella 80/100w bulbs and the difference is amazing, especially for the cost. Much-improved low-beam pattern and much better "seeing distance" on high-beam. No problems with the high-powered bulbs used on two bikes in the past 12 years, but if you use high-wattage passing lamps you may want to put them on a relay since they are wired into the low-beam circuit. The 80w bulb adds 2A to that 15A circuit which may overpower the fuse, but stock passing lamp bulbs shouldn't be a problem.
Cibie is another E-code option, but I selected Hella because they cost half as much and are equally high-quality products.
It's amazing to me that more riders haven't discovered this low-cost way to improve headlight performance.