First of all, let me say, I can't imagine how hurtful all those years of rejection from your W have been. My heart truly goes out to you, and I can understand your anger and wanting to classify her as abnormal in some way. Hell, all of us here do it. And she does have obvious psychological issues, but they don't sound narcissistic or shallow to me--the behavior you describe sounds more like deep insecurity. (I majored in psych as an undergrad, so I'm not talking totally out of my butt here. ) You say she can't empathize with you, but neither of you seem to be empathizing with each other much.
I have question--do you think you would have stayed and put up with your W if she wasn't as hot as she is? If the answer is yes, does she know that? And if the answer is no--don't you think she knows that and it terrifies her?
What do you love about your W, other than the way she looks? How do you support those things in her?
If you see her as the temptress, always in control because of the way she looks on the outside, I think there's a lot you're not seeing. Heck, her insecurity about her looks could be a factor in withdrawing from sex--she might be terrified that you will see her physical flaws, so she's overcome with anxiety and can't enjoy it, so she avoids it. The constant searches for anti-aging creams tell me that she is acutely aware of her flaws.
I think her need to maintain some kind of perfect beauty to maintain what she believes makes her valuable as a human being--that can take priority over you, your M, sex, everything. If she believes you love her primarily for the way she looks, then she may be actually trying to preserve your love for her by NOT having sex with you and showing you her flaws.
You said that "what worked" when you ML has been some kind of finality, some kind of ending. It would make sense that THAT would end her need to hide her flaws from you. She can be "free" temporarily from her insecurities about you seeing the real her and risking losing you--cause you're already lost.
I'm not forgetting that she also has this "grass is greener" curiosity going on at the same time. I think you can reignite her spark on this pretty easily (lots of sexy ideas already given to you).
Convincing her that you love her no matter how she looks, and her believing that she is worthwhile no matter how she looks--those are the humps you need to get over. I think counseling could really help you on that, and I'm glad you guys are getting it.
It is in the shelter of each other that people live.--Irish proverb
) You say she can't empathize with you, but neither of you seem to be empathizing with each other much. 
