From my limited time here I don't see herbs drop frequently enough for those who would use them in quantity, I see maybe 0-3 on most contract runs and each is worth maybe one use of water, varying in quality depending on heal skill.
I think adding an herb to each rest or reset of a medicine man/physician rogue (pure)/apothecary would go a ways towards helping them out.
This would result in 2 for the dedicated support healer rogue per rest/reset and 1 for the medicine barb where its more of a side benefit.
Herb Bundles will drop quite frequently and each bundle has between 4-12 herbs in it. They're usually just littering the charity chest too.