For some of us, wearing a skirt to Church is a sign of humility and devotion and there is nothing wrong with that. If the woman wearing a skirt wears it to show respect and humility, then that is what it means. Although some argue that a skirt is a sign of oppression, a skirt degrades a woman only if she believes it to do so.
You can’t say that a symbol means a specific thing and then deny a person’s ability to say it means something else to them. Isn’t that at least part of what feminism is supposed to be about, defining our own symbols and what they mean rather than letting others define our symbols for us?
The skirt is only a symbol of repression because a person chooses to see it as such. The idea of wearing a skirt or dress is not a sign of humility and devotion only to the woman in question. The Church asks us to wear skirts and dresses to show respect. There are also groups of people who say that skirts and dresses are signs of repression. Therefore, there are two entities with two very different symbolic meanings behind the dress. You cannot intelligently take one person's meaning and apply it ham-handedly to another person's symbol and say that A must mean B's interpretation. It would be like saying that the symbol of stars on the temple is a sign of devil worship. That is not why the stars were placed on the temple. That is not what they mean.
Some women choose to accept a skirt and/or dress because the Church leadership has asked us to do so as a sign of respect to the Lord and His house. You cannot assume that means repression if it does not mean repression to that woman, just like you cannot automatically assume that a woman who does not choose to follow that request is doing so out of defiance.
To answer the question in the title:
There may be nothing eternal about the physical skirt itself, yet there is everything eternal about the decision whether or not to wear one to church or to the temple. That decision is between you and God. Either way, no one else can accurately judge your, personal, reasons for your choice. (Although there will be people who try. The mature thing to do is to realize that and not worry about it. That is between them and God, ultimately.)
In the path of discipleship, Christ often asked people to sacrifice something. He did not ask everyone to sacrifice all their possessions, but He asked it of the young man. Why? It is because the young man's riches were important to him.
45 Again, the kingdom of heaven is like unto a merchant man, seeking goodly pearls:
46 Who, when he had found one pearl of great price, went and sold all that he had, and bought it.
THAT is what is required of discipleship. That is required when making any decision like this. For me, I am seeking salvation. Now that I have found the way of salvation, I will gladly sell all that I have: my own feelings of comfort, my own sense of understanding, my pride and my pain for it. To me, wearing a skirt might seem uncomfortable and silly, but it is worth membership in that Church with the true Gospel of Christ.
And isn't a sacrifice that pinches a more poignant symbol of devotion? To the woman who finds a skirt comfortable and would wear a skirt anyway, the sacrifice is a meaningless one. But, to a woman who feels it is a sign of humiliation or degradation, being willing to wear a skirt on the word of a fallible (male) human, simply because the Lord Christ has shown His support of that human as His mouthpiece, is a beautiful and powerful testament to her willingness to humble herself before God and do all that He asks. And, as those and similar small offerings of sacrifice, humility and devotion are made, the soul of that woman is changed in ways she had never dreamed. Her sacrifice becomes strength, her questions about her worth in the eyes of the Lord and His servants become answers and she truly learns what it means to be His daughter and what it means to be a woman. She learns that no mere skirt can lower her into the dust, for God Himself has made her His Glory.
That is what is eternal about a skirt.