I suspect it's because it takes some work to collect the guano + it speeds up growing times on herbs and crops. yellow crumb takes longer to grow + when you eat it, or imbibe in its essence, it speeds up learning time for whatever skill you are learning. Which is awesome when you have a skill that takes 52 days to learn.
If you have all of the upgrades (both for herbs and getting more at the vendor) you can make a decent amount of currants from shucking the yellow you grow and selling the seeds to the tool vendor
Guano has always been worth a lot of money, even before the current practice of farming industrial quantities of yellow, since available plots were scarce, thus making the 90% reduction very valuable.
About 10 months ago someone tried to crash the guano market. It didn't work.
At Herbalism 3 the avg shuck will give you 2.4 seeds per flower. Meaning 130 currants per flower is a fair price. IF you only have H1 or 2 you'll prob make more selling the flowers on auctions or towers rather than shucking yourself.
Posh about 1.2mil if you sell flowers when you have all the herbalism & vendor upgrade & 1.4 mil if you suck and can get on average 2.5 seeds per flower.
elf, the question was why it was worth so much. telling someone that it sells for a lot of cash doesn't explain why it's worth so much. telling them it gives you a lot of IMG when donated does explain it in part. just be nicer next time, please.