As a Christian, God is your Father and the Bible makes it known that He is interested in every aspect of the lives of His children, right to the seemingly insignificant details. The Bible says that he has numbered the strands of hair on the heads of men. This clearly proves that God never misses any detail. He is omniscient. How you dress would, of course, matter to Him.
Looking back to the story of Adam and Eve, the couple had covered themselves up in leaves but that was not good enough for God. He was interested in their dressing; he clothed them. Perhaps because of the weather, the Bible didn’t specify, but He did clothe them. It mattered to Him.
The truth is that God might not care about how you are dressed when it comes to your relationship with Him but you can be sure that He is concerned about what is in your heart that makes you dress the way you do. He is concerned about the nature of your heart; who you dress to please.
God transcends time and His works are not limited by the physical. Yes, He does not look on the outward appearance of a man, as seen in the story of David, he looks on the heart. Yet, it is true that what goes on on the inside influences what is shows on the outside.
So, of course God cares about how you dress. He cares about who you are dressing to please and the intents of your heart when you put on whatever, whether it is decent, shabby, rough or however.
Work on the inside. The outside will reflect it, eventually.