Ok well I'll re-comment.
1. I said very slightly, as in probably not a full mpg. The lights need power from the alternator, which needs power from the engine.
2. Yes they do run at 2 volts below system voltage. They will have a lifetime in hours, so use it as you want. During the night or constant.
3. I don't understand how that deems the headlight assembly crap but the turn signal lamp housings fine.
Here's a good craigslist example. I found this on the first link I clicked, I'm not kidding. Look at the headlight and the parking lamp, only the headlight is really fogged. Same plastic, same exposure to natural elements. One had a light on constant, one didn't. I don't know what else to make of it.
4. Yes the parking brake does disable it, but when pressing the parking brake on a car that hasn't had it pressed in years, negative things may occur, like dragging for a while. Mine did that when I first hit mine, but I waited to test it until I was about to do a brake checkup, so I used lithium grease on where the lines enter the shielding.
DRL's can help in very few situations. But remember not all cars in our GP's time came with DRL's, and it's not a law in Michigan. It's just my decision to have them disabled, If I was concerned about things like those extremely rare situations, I'd wire my parking lamps, or fog lamps as the DRL's instead. Or just turn them on on my own. I'm much more worried about getting into an accident from other people's stupid decisions or mistakes, not from my headlights not being on. But with a car like my color in the winter, you cant miss it. Even in the summer, it doesn't quite match anything else. Red, silver, light blue, or gold GP's are hard to miss in any good weather. It's all about opinions.