Fun idea. I think I have another one which I haven't seen anyone mention, since costumes are being included. I'm going by memory, so I may not be right.
Barnabas has a maroon either robe or smoking jacket that's seen a few times. It looks for all the world like the same one Quentin is wearing in a confrontation scene with Magda on the staircase in Collinwood.
This is the scene [spoiler]after he is cursed, and has gotten just about falling down drunk and is insulting her and she him. He ends up sitting down hard on the stairs and starts saying, as if surprised by it himself, how much he loved Jenny.[/spoiler] Again, its been a while, but it sure looks like its the same one.
Another scene is in 1840, but I don't remember which episode. There is one scene with Desmond and Quentin where they seem to have changed jackets. The colors are reversed, and Quentins sleeves look REAL short all of a sudden.
Jeannie