Guild Wars 2

Since I have absolutely no interest in making the Mysterious Vine back piece, do I need any of these?

Mysterious Seed
Ley Line Infused Stone
Vial of Sacred Glacial Water
Pile of Phantasmal Residue
Chaos Orb
Pile of Ley Line Dust
Enormous Foxfire Cluster?

Is there something else, other than trashing them, that I can do with these?

if you don’t bank your silver arrows, you’ll never be able to defeat ganon  :\

I kinda had the same dilemma – throw them out or keep them in case i start crafting in the future and want to make that back piece? But then i thought: i can get these items again, anytime with different characters, so yeah…. i think i’ll just throw them out :/ Feels a bit bad though…

Yeah. That’s what I was thinking. Can’t sell them to a vendor. Can’t, ‘natch, sell them in the TP. Can’t convert them into something less a pain in the butt (would be nice to be able to chuck them into the forge to get something else).

I would like an Anet response on whether or not I should keep these items. Will there be a use for them in the future, other than for this backpiece? Will they be tradeable to a vendor?

They’re never going to be tradable. You can get infinite numbers of these items, some via dialogue options to the various relevant NPCs inside the instances, some for a small laurel cost from Dry Top NPCs, ect.