Ok, I've been running with these lights for a few weeks (I decided against replacing them). I kept them because I saw the lights as a good platform to modify from.
I did discover the lights can be adjusted horizontally by losening the screw underneath the lamp housing. I played around with it a bit and found there's not really any improvement in adjusting them at an angle. Straight ahead seems to work best.
My plan is to modify the whole system. I'm opening this up to comment to see if anyone has any thoughts and suggestions.
The lamp housings take MR11 bulbs, which you can get in a variety of voltages, wattages, and beam spreads. I'd like to upgrade the voltage from 6V to 12V and go with 12V bulbs. My idea is to go with two 20 watt bulbs. One will be a narrow flood, and the other a spot. If anyone is interested in the technical details of the bulb, you should know you'll need a LENSED bulb (which means there is a flat piece of plastic on the front of the bulb) because the lamp housing doesn't have a lens. The lamp housing also uses a GZ4 base, so you'll need the MR11 bulbs that have the two small prongs.
10 degree Spot
20 degree Flood
I'll need to change the battery, of course. My plan is to build my own battery pack out of 10 NiMh D cells. I plan on soldering them together in series and in a formation which will enable them to fit inside a water bottle. This will give me a 12v battery. I thought about using 11 cells for 13.2 V which would increase the light output at the expense of bulb life, however I'm already going to have 40 watts total, so I've decided against going with 11 cells. My goal is to get at least 5000 maH, which should give me about 1.5 hours of run time. If anyone knows of a cheap source for NiMh D cells, this would help as they seem to cost about $9-10 each. I could go with C cells at the expense of about 30 minutes of run time. My commute takes just under an hour, so 1 hour of run time is cutting it a bit too close.
I haven't done much research on a charger. I'd really need a smart charger since overcharging NiMh cells will ruin them. If anyone has any good sources, let me know.