I think that a different understanding of the Rav Miller’s precious advice will answer many of the issues that people brought up. I don’t think that he meant that the husband should bribe his wife. Perhaps he meant that the husband should demonstrate to her in a clear and kind way, how important this issue is to him.
For some husbands and wives, a diamond ring is a significant but attainable gift that will show the wife that the husband both loves her and very much wants to see her change the way she dresses. For others, it will take a more expensive gift, or OTOH maybe just sweet words alone without needing the large expenditure.
This understanding explains why the advice is not insulting to the wife, not too expensive to afford, or too cheap to be meaningful. Each husband had to use words and actions that are appropriate to deliver the Rav’s message – “I love you, and I just want you to realize that this is important to me.”