After all the notes are memorised I move on to the next piece. Even if the piece is not played at a Performance level. I feel it is a waste of time to linger on a piece you have totally memorised hoping to force improvement in the expression. You just will never be completely satisfied. One of my teachers said to me, "A good artists knows when to stop." Which i disagreed with at first because of my perfectionist attitute, but now I start to agree. Because a good artists knows their limitations, knows when to stop "obsessing" over particular points, and just lets their art flow. Sometimes if you obsess people can hear that in your playing, and things start to sound fake, overdone, weak.
I don't think that pieces I have memorised ever are removed from inspection and upkeep/maintenance with regard to expression. I like to think you play music differently today than what you will tommorow, maybe not that much of a quick contrast, but on the same track. But I do believe there is a time limit to the time you spend memorising notes, the physical playing, the expression never ends, if it did I dont think I'd ever play music.