Read the quote again, darx, and you see that Brandon says ANY allomancer with access to steel or iron could learn how if they tried. That means little weak mistings who can only burn iron as well as full mistborn. It's not in the power, it's in the control they have over their metal. There is some trick to it. This is why vin doesn't go into matrix vision as you called it. She could see the lines to the bracers because she was powerful enough to pull on them, the blood didn't block it anymore. Seeing trace metals as the inquisitors do would not require power, just skill.
Avalon, your theory makes sense to me, though I still feel it is too similar to allomancy and feruchemy. Brandon has emphasizes multiple times that hemalurgy is its own magic system.
I did just notice though....Brandon says earlier in his MB1 annotations that only very powerful allomancers could pull on metals inside someone's body. This seems to conflict with the quote I gave. Any ideas on how they can both be true? Or did Brandon mess up (yes, I know, blasphemy)?