How much of our struggle should we share with our wives, and how much should we keep to ourselves?  Or rather, how much detail should we go into when discussing this topic with our wives?

Also, if our problem is hyper-sensitivity to lust, then is marital intimacy also supposed to be super-tznius, or not?

In many cases, your wife need not know the extent of your struggle, just that you have a normal male y"h.  But that's not an absolute rule.

You're probably not ready for "super tznius" in marital intimacy.  I would stick to the Ikar Hadin without any Chumros.  If necessary, seek guidance from a Rav who understands your Nisyonos.

If you are doing well in your progress, no need to tell your wife. If you keep having slips, on the other hand, letting your wife know can be a big help, albeit a "painful" medicine. But this should be done in the presence of a therapist who can explain to her the nature of "lust addiction". She can then become your accountibility partner. However, even in such a case, it is not neccessary, nor helpful, to share "too many" details of the struggle with her. She doesn't understand this "disease". But she can sense your emotional stability and contentment. Let her know how you are doing in this area in general terms...

As far as marital intimacy, it is true that we are addicted to "lust" and therefore, if you can refrain from lust with the wife as well, to the extent possible, this can be helpful. But take things one step at a time. Try to take on too much at once, and you may lose it all... But this is a good goal to aim for down the line. The most successful 12-Steppers will tell you that even lust with the wife is not healthy. Aim for emotional closeness and intimacy over the lust aspect of relations.

Dear Eye,
Please see my personal message about your post above. The big issue in my case that at least partially covers your marriage concern as well, is: what "mode" am I  on? Giving, or getting? Nothing here to do with "good" or "bad" or even what is "nice", or "better" - just what is the truth: It really works wonders to be aware of it. The following, Rav Dessler brings out in Kuntres Hachesed, but I write it here be"H from a program perspective:
Does this make sense to you:
If I am truly primarily concerned about what I am giving to all the people in the world, to the people on the street that I'm walking on, to the folks in my workplace, to my family, to my wife...well, then a lot of things are gonna be OK. Like how they look, what they are giving me, how they make me feel - "Hey! What good am I doing for that person in the street I am staring at? I'd better daven for them - Hashem certainly has some kind of purpose and/or plan for them even if they are a goy, no? They need something! (and it's surely not: my ogling at them!)"...
Are my kids making me feel proud or secure as a parent w/their behavior, or are they 'driving me nuts'? "Hey! What does how they make me feel have to do w/what I can give to them? Better I should look at how I can be useful to them given my proclivities to anger or insecurity. Now I am getting somewhere...
Is my relationship w/my wife fulfilling, or not so..."Hey, now, is that why she married me? Is that the only reason I married her? If she'd give me all the fancy stuff I desired (including the lust) would it satisfy me? What would really happen then?" This takes some quiet real thinking time.
I am not speaking out against satisfaction in every aspect of marriage, but I need to face this fact: Am I really looking for physical satisfaction, or for something else in her - like being truly deeply and fully trustingly connected to another person in this short life - with no price tag either way - just because we are one? Yup, for me that is definitely it. And the only way to "get" that is by giving it all away for free to her, no?" After all, do we really expect anything less from our wives? You may be able to apply this idea to your issue and approach it from the angle of how whatever you do or choose to communicate w/your wife, etc., gives to/affects her. If you try it let us know what happens, OK?
If this was helpful to you, fantastic!! If not, nu... It reminded me of how precious my relationships really are to me and maybe I'll smile just a bit more when I walk in the door tonight!  
Love,
Dov