Don't you feel like the game should not be in the eternal state of everything? Ever since the Runescape, people who participate in Xmas event get their hat/emote/costume, and it is kind of the badge that you did it. I am not exactly familiar with Gears skins, but you are calling it a vault, which implies the cyclical nature, like most games. You will have your season vibe skins (Summer, Halloween, Winter, Esports etc.). I think most progression system do it "right", and only hoard the cosmetics that have symbolical value. The skins themselves can be trash, but they can work as a piece of history: I have played the game since 2010, I have got it on launch, I played in Season One, I supported X charity event, I completed X challenges etc.
I don't think I will ever regret not having some skins in the game I don't even play anymore. Give me a straight answer: would you pay $15 right now just for that vaulted Gears skin?