Costume Crate and/or make costumes "collectables"
I agree with the fact that costume gear needs a non-inventory home. This is especially true since the bank is shared between all characters you create, so I can’t store costumes on an alt. I believe the best idea is to make costumes collectible like the mini-pets so that they can be stored and traded out at appropriate moments.
How about we just carry ALL town clothes on us at all times? And just have it take no space. It isn’t like having unlimited weapons or consumables or armor. It is like a dye, it’s just for show.
I would also like a place to stash hats or costumes that I don’t want to currently wear. The festival NPC from GW1 was a great help in storing my hats, so that I could wear them when appropriate and not worry about filling up my inventory. A collectible section for them would be fine too (or a closet?)