I've got a better idea.
Why not both?
Yorica gives us both random armor drops and specific ones we can trade wings for.
Why not have a single stone provide a random augment, but, say five or ten of those stones (with an according multiple of bayld cost as well) provide a "best case" augment of choice for the tier?
I do a bucketload of Yorica and end up with 5 +1 Verdigris Stones. I blow all five + 2500 Bayld and get a best-case +1 augment of my choice on an armor piece instead of a random one for a single stone + 500 Bayld- or I can take my chances with a single stone.
People will still be doing Skirmish for tons of stones as a result.
Edit bonus: Let people trade in unaugmented armor pieces for a stone- hands/feet for NQ, head/legs for +1, body/shield for +2. Now nothing goes to waste even if it's useless!