At the moment, crafting is pretty boring. Insert X,Y,Z, get A. The only variation in this pattern is the small chance of getting a Unique Variant.
I'd propose adding items which one can add to a crafting recipe to add bonuses. Perhaps someone wants to craft a Nightblade for running the Jelly King; goes to a crafting terminal, selects Nightblade, and, oh look, he has a Jelly Hunter's Essence! So before clicking Transmute, he throws it in, and his Nightblade suddenly has a shiny "Damage vs Slimes: Low".
Or another player might have the extremely rare and valuable Thunderstone Essence - slight chance of inflicting minor shock. Of course, even being so rare as it is, everyone running around with Status Effects on every weapon would be a terrifying sight, so this one might have only a 33% chance of working.
To make things more interesting, these items could carry possible penalties - Deepfreeze Essence? Fire Resistance: Medium. Minus Freeze Resistance: Low.
I like the positive-negative idea because by having the player influence the input, you make alchemy more interesting and a little more diverse.
Meanwhile in Profitville, you've got to consider that a lot of people mass craft low star items for a chance at receiving a Max/VH UV, so people would use these "essences" - as you call them - to greatly increase the frequency of UVs resulting in an increase in the amounts of UV gear, making them less rare and "Unique" causing an increase in profit to players who would use this feature for those reasons.
That would essentially give more players more crowns so in theory, the CE prices would rise because there would be more players with money that are able to spend that (using 10k as an example for the literal people) 10k or so that they didn't have before on a couple hundred CE resulting in higher demands for CE because there would be less of it.
But this is all of course, speculation and theory, so in conclusion, I like the idea, it'd make the game a little more fun when crafting and change up the combat mechanics by allowing you acquire new stat gains/losses that weren't previously available.