This really doesnt have to do with Tznius and I dont like that it gets lumped together, because it just turns girls off from the idea of Tznius altogether.
If you can wear a designer label and still be tasteful and tznius GO RIGHT AHEAD, part of being Jewish is being a light unto the nations and to constantly be making a Kiddush Hash-m. When non-Jews see Frum girls out in the world dressed tastefully and not in some shmatta bag with their eye brows covered they see that we are normal yet refined, and I believe (for whatever its worth) that is a Kiddush Hash-m.
If you want to say that we are Goshmius hungry, that I agree with. But dont say its a tznius issue, because its not.