Is there any way to quickly see if you've already got an item in your wardrobe before buying it? (Other than searching for it in your wardrobe)

If you know what item you're potentially going to buy, you can do an account search for that item (either using the account search page or by hovering on the item and clicking account search there). That will tell you if you have the item and where it is (like in a shop, your vault, wardrobe, etc.).

Perfect, thank you!!

Digging your HA, btw =]