Oh dear, I note already an error in my interpretation. Oof.

According to Plotinus (and Taylor, as it happens), it seems that Psyche's descent from the lofty mountain to the beautiful valley is, indeed, a "first" descent of the soul; from there it can stop, or it can proceed to descend further and further down as far as it will.

Now is not a good time for editing this, but I'll have to revisit once I've reread and reconsidered this more thoroughly...