As you pointed out, Mistborn aren't as powerful in any one area as their Misting counterparts, yet they still have their specialties - I was hoping to rectify this by giving them the first 4 or 5 class abilities from each Misting class, then allowing them to take a "focus" in one area where they gain an additional 2 or 3 class abilities in that area.
I realize that Wizards is mucking up a fine system with the release of 4.0, but since it's not out, and it's looking to suck, I've based all of my notes on 3.0/3.5. I do hope to get a little input from Brandon about this, as I'm a bit confused about a few things too - the costs of metals and burn rates as you said, but also the quantities in which they ingest them, and what the units of measure for the world are.
One of the other things I wanted to do some work on is other races such as Kandra and Koloss, I imagine that playing a Kandra would be easy enough, but Koloss and Mistwraiths would end up as montsers most likely. Another thing I'd like help from Brandon with is what other kinds of creatures exist in his world - farm animals, dangerous beasts, etc.
Pewter - reduces damage, increases STR, DEX, CON, and land speed. Prolonged use inflicts subdual damage after.
Soothing/Rioting - higher level means higher DC to resist, or higher maximum area of effect.
Tin - competency bonus to Reflex saves, pluses to spot, search, listen and survival checks, and rerolls/bonuses against concealment, etc.
New feats and the like would be useful as well...
Input plz? lol.