You guys rock, thanks for all the helpful input.

So, the HiJack functionality is to be dimmer with the headlights on (at night). Thanks for clarifying. Was it designed with the following reasoning?
"Dimmer with headlights on because it's easier to see the buttons at night"
"Brighter in the day to overcome the sun light"

If that's the logic, maybe I'm just using it wrong by wanting the VFD and buttons brighter at night.

Also, in response to oliver and Bitt, HiJack DOES have two independant buttonled levels (similar to the VFD dimmer; for headlights off and headlights on), right? As far as I tested, it seemed like there were independant values for lights on and lights off. And in my tests, I varied the settings drasticaly to overcome the "half as bright with the lights on" factor. Did I come to the wrong conclusion?

But Mark, a thought about the parameter and formula for dimness. Maybe it would be as simple as:
if (headlight_sense_is_active())
brightness = (brightness + 1) / (2 / buttonled_factor);

In config.ini, buttonled_factor could be 1, 2, or 4. Essentially, it would control the amount of change in button illumination (with illumination level value constant) between headlights on and headlights off. buttonled_factor=1 would cut the brightness in half when the lights were on. buttonled_factor=2 would leave the buttons at the same brightness regardless of headlights. buttonled_factor=4 would DOUBLE the brightness when the headlights were on (if that's even possible).

Default to 1 to retain the old functionality. If people want to avoid the 50% reduction, just set it at 2.

::shrug:: Just a thought. I'll keep playing with it. Maybe dimmer at night and brigter in the day IS better.