Zopiclone is just a mix of the active isomer and the non- or less-active one. Since the dosages are about twice as high between zopiclone and eszopiclone, and the binding affinity strongly favors one isomer over another, you've got a decent amount of a substance floating around that may or may not be interfering with other receptors. That's got dirty drug potential written all over it.
Just buy the active isomer and take the minimum effective dose. Why fuck with the good drug and its goofy cousin at the same time?