I have a neighbor who I could see this working for. Personally my husband and I wouldn’t take that approach because in a sensitive topic, you have to be very careful with how you say things or you are less likely to be effective and more likely to be lashed out at.
In this case, the attitude I feel coming across is I am perfect and you need to work on yourself and I’m willing to pay you for it. See how generous I am?
I think this is usually wrong and that’s why I’d find it offensive. As has been brought up before, usually people marry a spouse with a compatible level of yiddishkeit, so if he found her less than tzniusdik look attractive, then he is part of the problem and shouldn’t be playing tzaddik now.
What would be taken much better by me, would be something like, “Chanale, I know when we got married, this is how you dressed and I was fine with that. However, you’ve helped me grow so much that now, your way of dress bothers me. I know it would be hard for you to change so can we make a deal? I will stop watching movies/non Jewish entertainment, or some other comparable kabbala, and you will go shopping, and buy a new tzniusdik wardrobe?
Here I would feel motivated because a) we are in this together and if it gets hard for me, I know he is working hard as well.
B) he is not making himself look good at my expense.
C) I get the zechus of helping him improve as well.
Disclaimer 1: I dress tzniusdik and my husband doesn’t watch movies or sports
Disclaimer 2: HaRav Miller said you have to know who you are talking to so I am not in any way negating what he said, as this is included within that, I am simply giving another approach/example.