Optional Items:
I personally am a real fan of vanity items in MMOs and I feel that great improvements could be done for this section. First of all, whenever there's a bunch of new items added in to the store, it's an huge chore to buy all of them individually as you don't have "Shopping cart/basket" kind of a feature which would let you purchase multiple items at once. This is emphasized by the fact that the cost per item usually is quite low. Each purchase also requires multiple steps to actually confirm it, which again emphasizes the issue.
In addition to the purchase process, I'm also puzzled why there aren't more items in the Store? I'm sure many players would be more than willing to get more new mounts, clothes, hairstyles and such as optional items and I think it's a great way to offer users what they want and at the same time give the game team a nice revenue wise boost to help them make the game even better!