A spot of washing-up liquid wiped over the mirror and then polished off works ok: the detergent zaps the surface tension of the water globules that make up the 'mist' leaving the mirror clear.

And from one CX500 owner to another: it also works for visors!
An article in the 'Motor Cycle' from around 30 years ago suggested wiping the cut face of a potato across the visor and then polishing it off. I didn't try this, prefering to eat the potato in chip butty form.

John