If there were more of them, they wouldn't be rare.
Equipment tiers are already planned, but there's this whole "rebalancing" project that no one wants to touch.
What part of rare
drop don't you understand, the rusty version would not devalue the normal version as they are inferior, nore would they affect balancing as they are weaker than the normal versions. If fine
has a (0.02%) drop rate from a jacko, Snake Lord, or a reaper I don't think your going to see a lot of people running around with them....
You don't need to re-balance so long as the range between rust and fine is not out of control. You could release a lot of the unreleased weapons and armor as in-between inferior versions for the time being that way not everyone will have the same stuff (this would make the game infinitely better in my eyes).
Why not have ragged assassin boots that doesn't have any state bonuses or a rusty Falchion that is little better than a short sword that people can find very rarely from monsters?