I think the tarlok gem's really gave an edge for the legendary and epic items. Maybe different gem recipes can drop from copper, silver or gold chests with something similar to Tarlok's gem recipes which means:
- recipes are non-tradeable
- but gems produced can be sold
- recipes can only be used one time (i.e. it's lost after a gem is crafted)

Here's a sample for stat bonus similar to Tarlok's gems (ofc dev's would know better stat distribution based on current class balance), but just to give an idea:

Copper chests:
Wisdom: 1 int
Wind: 1 dex
Rage: 1 str

Silver chests:
Wisdom: 1 int / 1 str
Wind: 1 dex / 1 int
Rage: 1 str / 1 dex

Gold chests:
Wisdom: 2 int / 1 str
Wind: 2 dex / 1 int
Rage: 2 str / 1 dex

Elite Gold / Locked Crates:
Wisdom: 3 int / 2 str
Wind: 3 dex / 2 int
Rage: 2 str / 2 dex

Hopefully, this would also put back some value on chests and actually be farmed...

-rasi