You really don't think it's a legitimate goal that she "gets" the message? That she agrees it's a legitimate issue? Are you saying that because of who she is (at least, who she is according to my descriptions of her), or because it's just not generally a legitimate goal to have your spouse "get" something that is important to you.
If it's the former, that expecting Ms.Hdog to ever "get it" is folly, then I understand your statement. It may be folly. But I can't use that expected reaction as a way of avoiding confronting her with this.
Perhaps "realistic" is a better word than "legitimate." It's certainly within reason to expect a spouse to "get" a message, but in your W's case, if you actually set that as a goal, I think you will wind up being sidetracked while she attacks the "legitimacy" of your wanting her to get you. Did that make any sense? And yes, this is because of how you have described her.
I do not think you should go into this expecting to change her mind-- only to change her BEHAVIOR. In the first place I don't think you CAN change her mind. And in the second place, if you did, she'd have too much pride to let you know that you did. (Notwithstanding the "I'll be a better wife" convo.)
Hmmm... that gives me an idea. What if you approach it this way: You remind her of that statement, not in a "throwing it up in her face" way, but in a thoughtful, sensitive way. And then you say, "Here's how you can be a better wife: commit to s once a week. Even if you don't agree that it is a good idea. Even if you don't agree that it is a 'legitimate' want of mine. Just agree because it is a way you 'can be a better wife.""
Then stop. Don't defend, explain, convince, justify. This needs no justification. Clean, clear, no underbrush to hide behind.
And when she says "that's ridiculous, you can't ask me to do something like that that I think is silly and worthless," don't say anything.
Come back over and over again relentlessly and gently to the theme: you said you wanted to be a better wife-- here's how you can be.