Mepal,
It might depend on your tone and manner of expression. It’s hard to convey that in blog comment. In fact, I have used similar lines (they come out stilted when written, and my examples aren’t exact) and the outcome has been exactly as Squeak predicted: the individuals complimented go out of their way to approach me when wearing something tznius, and I have formed close and warm relationships with individuals with whom I had previously had more casual neighborly (but warm) interactions.
Most women truly want to do what is correct, and admiring them for tznius choices supports this desire and decreases the voices urging more and more inappropriate and revealing clothing (unless one always has voices in his head, in which case I would recommend a good psychiatrist :))
Squeak, I was actually quite flattered when I saw I was mechavain to you! 🙂