So... I've heard that there's actually an achievement involving these... does anyone have any insight on the matter?

i honestly dunno. i can't think of an achievement with them.

I've looked through all the achievements under the tab, but I can't find on concerning it.. So it might just be a rumor... : )

They were used for the Recycle beast Achievement,and if the Beast use's them again then use the item.

I think someone suggested it... I remember seeing that somewhere

May have been me you saw suggesting it. There's a sticky in this forum for achievement suggestions, and I'm betting that's where OP saw it, too. Otherwise I don't know what "rumor" they're speaking of.