This was used to make the Plainswalker bow after PoR was released, then the bows were nerfrd, Plainswalker was removed, and now calming fluid serves no other purpose at this time except to skill up in brewing. Not sure what it sells back to vendor for, but you can bet it isn't much!...Just a little heads up..
Who would have thought, twelve years later, that someone would read the information you provided and have been so pleased to find it? At the time you wrote it, there probably wasn't even such a thing as the Extraplanar Trade Satchel! And yet now, in the future, we're running around with containers that we order such as to ensure any collectible ends up in the Deep Caverns Collector Case rather than take up bagspace elsewhere, and in the same way, anything with the tradeskill tag ends up in the aforementioned satchel, to be counted against some meaningless combine that will improve our Artisan'z Prize. To find a description like yours, much to the effect of "this once had a purpose but now can safely be discarded the moment you find it" is nothing short of blessed relief. Thank you ever so much.