This old screen-shot got me thinking....

When I look at that pic, I am intuitively compelled to use my mouse to scroll through those top three cards (moving mouse to left and right). And it seems natural to click on one of the five card decks, to select which spell group is available for scrolling.
Spell Deck UI in action:

From the world map UI, user clicks a_single spell icon and up pops the spell deck UI. User clicks the deck which contains the spell type they are looking for. Then scrolls through the individual spell cards to locate the spell of their choice. Right-click the spell card to get more info. Double-click the card to cast it. Spell decks would allow users to narrow down their search. I find this preferable to clicking through a long list of tiny spell icons in the main UI.
To further function: Users could assemble their own spell decks. They could organize spells into groupings/decks which best suit their methodology. I may want to organize my spells into Enchantment, Offense, Defense, World Shattering, Most Commonly Used etc. Other players may want to organize spells by shard type, or help/hurt, or casting cost, or whatever works for them. Point being to speed up spell selection by narrowing the search into groupings which best suit each individual player.
Would be nice if players could mod the look of their spell decks. That way they can add symbols, colors, and/or text to quickly identify which deck contains what. Heck, why not shoot the moon... give players the ability to also mod the spell cards. Then they can add whatever info is relevant to them. A right-click could bring up all of a spells info; while the card itself could contain only that info which the player wishes it to. ??