It seemed to me that a lot of attention was given to herbs when they first appeared. I found the seeds to be quite difficult to come by and actually bought 3 purple flowers on auction for 750 currants, not knowing what they did. Once I finally got some seeds, I had a hard time finding open plots in the public herb gardens in which to plant them. So I moved my house to a swamp-bog so I could have my own herb garden (and also barnacles and fireflies). Now that I've tried out the different herbs, I have to think that they really aren't worth the effort. Let's review:
Gandlevery: A small energy boost, could be of use to low-level Glitch, but no replacement for some good food.
Hairball: Faster walk speed, a unique buff, probably the most valuable herb for situations when you would rather walk/run through a few areas than teleport.
Purple Flower: Pretty, but has no actual benefit, essentially valueless.
Rookswort: No mood loss, I can't think of a situation when I would need this.
Rubewood: Improved chance for drops, how much? 5%? The times I have used this I have received few or no drops from typical actions.
Silvertongue: Bonus on next quest or achievement, but it is only 5%, which is hardly anything.
Yellow Crumb Flower: Double learning speed, for one minute. I suppose if you had a huge amount of these it would be of some value, but I think donating to shrines for favor is probably more efficient.
So the herbs are of very little game value, and at this point the herbs and their seeds don't seem to have much auction value. They are already old hat even though they've only been in existence for a short while. BUT, have they ever been needed for a project? If they became common project requirements, then their auction value would skyrocket (assuming that they would remain un-buyable from vendors) and the swamp homes would gain demand (currently, I am the only resident of my block of ten homes in Ivalo Trims).