I remember back when the CHMSL (center high-mount stop light, or third brake light) first came out, it was because there was all sorts of hoopla about studies that had been done showing they reduced rear-enders. Turned out it was only 2 studies (they used taxis, I believe), but they were pretty good studies.
Problem was, the study results came out, and in a knee-jerk reaction (or a sop to the safety crowd) the government passed a regulation requiring them, and every car got them. And then they learned about the Law of Diminishing Returns.
What we learned after years of having CHMSLs is that the reduction in rear-enders observed in the two studies was NOT attibutable to the fact that there was a third brake light, or that it was mounted at eye level. Cars in the studies had fewer rear-enders because they had something DIFFERENT than every other car on the road. Humans are still animals, and animals respond quicker to something different in their environment than to something that is normal.
So now the traffic safety data shows diminishing returns from the CHMSL. Adjusting for all other factors, we have just as many rear-enders as we ever did, because now, practically every car on the road has one.
The only reason I know all this esoteric BS is because I wrote an article on this topic citing data from traffic institutes in Michigan.
So, regarding the DRLs, I think I can safely predict that, yes, you may see some marginal safety improvement from them now that they are new (at least here in the states). But when every car on the road has them, we'll be back to doing the same stupid things humans always do.
And, welfarewagon, all the other systems on a car that you cite - radio, wipers, turn signals - draw far less power than headlights. Headlights are the single biggest accessory draw. That's why this topic is relevant.
Rick