I honestly think wardrobe should permanently unlock for everyone who gets to a certain premium level, like level 3 or 4.
I think premium users need more benefits (i.e. getting a unique cosmetic item for certain days of premium membership -- 30d, 60d, 90d, 150d, 210d, etc) but they shouldn't be at the expense of non-premium players. They're meant to be benefits/QoL improvements. Perhaps each month there can be a new costume (for 400/800 NC) added to the NCStore and premium members get it for free.