Can't check my references to be certain (in Kentucky tasting and buying bourbon), but I'm pretty certain the trim was part of a package. And I agree, it looks better with the trim in my opinion.
True, it could be something that was damaged a lot. Looking at @Juan Veldez car, he has wheel opening chrome though that wasn't on all Challengers. That kinda of points to some kind of option, but without reference, I can't double check.
Both of my 70's have the front valence trim. I think it dresses up the front ends nicely on all 70-74's. Nice comparison to my buddy's purple T/A without it.