From your posting you come across as an angry man trying to tell himself that he is past caring. You sound angry at having wasted so many years waiting for change that never came, you sound bitter, disappointed and hurt as well.
Your wife does sound like she is trying though. This part of your post gave me the impression.
Quoting NOPkins:Tonight was yet another proof of the unlikeliness of any change occuring. I got turned down, and I didn't even ask for it :-) She asked me for a rain check, I said "sure, no problem". Then she asked me if I was going to be mad at her. I told her that I would not, and that I haven't been for quite a while. She countered with "it's only tuesday", which sailed right over my head, so I responded, "so, this means what" only to be told that it was early in the week yet regarding my ability to not be angry about our sex life. I walked away.
My point in the last overly dramatic paragraph, is simply that she knows the effect her 'failed efforts(?)' have had on me. That means that it knows what it is doing.
You will find that many ld spouses don't even want to try, nor do they want to talk about it; a denial that there is a problem with mismatch desires. At least your W is trying, have you told her that her efforts are not enough? If she knew how near you are at the end of your tether, maybe, just maybe you could both renew your efforts to resolve this issue? At least she recognises the problem but does she know how big it is? You said that you were near D years ago but you didn't mention much about the sexual issues because you felt sorry you were causing her so much emotional pain. Perhaps you should have told her then, or you should at least tell her now or you would be causing her the same emotional pain and confusion now 25 years on.
Although I am the HD spouse in my marriage I can't help but feel sorry for your W. I don't think its the fault of the ld spouse for the low drives but its the handling of it by both parties. Your W does sound to me like she is trying and so afraid of angering you. You need to let her know that what she is doing is not enough. You did not tell her this 25 years ago. Its never to late to tell her now.
Sex in a M should be fun and play, love, passion and excitement, an adventure/exploration, a special connection between two who love each other but sadly sex in a SSM is non-existent, a source of conflict, argument and stress, its work not play, its quick(lets get it over and done with and out of the way so that we don't have to think about it for sometime), its awkward (for having had too many arguments over it thereby raising the expectations of both parties). I could go on and on but I am sure many here can add to my definitions so I'll stop here.
I have no solutions Nopkins, just an observation and the hope that this will no longer be an issue in my M 20 years on! LH