[1] http://www.fda.gov/Food/GuidanceRegulation/GuidanceDocuments...
[2] http://www.nationalacademies.org/hmd/~/media/Files/Activity%...
So there's usually quite significant room for disagreement, especially as new evidence ever so slowly emerges. It doesn't help that trying to pinpoint a single number for each specific nutrient is a rather arbitrary goal.
Which is why the "balanced diet" approaches makes the most sense as a general recommendation--it's an affirmation not of what we do know, but of what we don't know.
I'm familiar with these issues surrounding vitamin D. There's no doubt it's essential, but the optimum intake and blood levels remains uncertain. Nonetheless no shortage of opinions are out there despite the uncertainty of findings backing up any particular stance.
IMO the problem in pinning it down is the wide range of effects of nutritional factors like vitamin D. Body systems are in constant flux, and need for vitamin D and optimum amount in circulation varies accordingly. The situation with trace minerals is somewhat similar when the mineral is an essential cofactor in specific enzyme-mediated processes--effects of low intake of the mineral element may not be easily observed from a whole-body perspective, and attribution of particular body manifestations to a mineral deficiency can be hard to establish.
I think that's the case with copper and other trace minerals and I don't expect the questions to be unequivocally resolved any time soon. Your idea of a "balanced", intake of diverse good quality foods is the only sensible recommendation we can make, especially since there's quite a bit of research showing merit of that approach.