My suggestion is simple. Let's say, for example, you need twenty Green Shards quickly, but all the reasonably priced Green Shards are in twenty separate auctions. That means you have to click each one, click the "Buy It Now" button, click the next auction, wait for the "Buy It Now" button to return to the clickable state, click it, and so on, keeping track as you go of how many you bought. Then, when you're done with that, you have to go to your mail and open each piece of mail, and accept them all. What I propose is both the ability to buy out multiple auctions at once, and a button in the mailbox similar to the "Mark All" button (or perhaps modifying that button's functionality slightly) to allow all mailed items to be accepted at the same time. The former suggestion seems like it could be a bit of work, messing with the UI, but the latter seems like an obvious and simple addition.

I apologize in advance if this has been suggested already.