By and large I agree with @Matt 11 about the woo, but in the interests of science I'd urge you also to look at the gelatin/collagen in the bone broth as a benefit entirely separate from the minerals. This is the protein that makes it "gell" (when you've made chicken jell-o, you know there's gelatin in it) That's why I drink it - I don't count it for calcium or anything else, but I want the proteins.
Analysis of bone broth has rarely been done, and it's naturally going to vary batch to batch, depend on a multitude of factors: water quality, time, amount of bone, type of bone, surface area of bone, quality of animal product, other additives used, etc… Of course, you can read up on it over at the Weston Price Foundation, but you'd get a very skewed, unsupported take on bone broth.
I ran across the article on the anaysis of beef bone broth: http://adc.bmj.com/content/9/52/251 Interesting that they compare in the end to milk of all things. And milk blows away the mineral content of bone broth.
Lead contamination in bone broth may be a concern: http://www.ncbi.nlm.nih.gov/pubmed/23375414
Chris Kresser had an article a while back discussing lead in broth: http://chriskresser.com/bone-broth-and-lead-toxicity-should-you-be-concerned
Over time, I've come to the conclusion that bone broth isn't what it's cracked up to be. Bone broth has a high 'woo' quotient. Broth is tasty, useful for cooking, is a good use of carcasses. But it is not a magic elixir that's extremely high in nutrition. I'm sure others will disagree, but that's my take based on the science available.