First, when purchasing items in bulk, after you shift click and get the quantity window, you can type in a number and hit the enter key to go to the confirm payment screen. Then if you try to hit enter again, you just open up your chat. I propose that the enter key works for confirming the purchase price as well.

Second, when you go to mend your soul, you have to click 'ok' on a dialog box that tells you how much you're going to pay. I propose putting that info directly into the Healer's "Mend Soul" click-option, and you simply click that one line to heal for the said price. This streamlines the soul mending screen, reduces the amount of clicks you have to make, and reduced the time spent as well.

Third, make the Auto-Sort Bags per-session confirmation box into a permanent UI toggle somewhere in Settings. It should have been there since it was introduced.

I know these are very minor and minute things, and the UI is pretty good as it is, but small tweaks like these will make it even better and more efficient.