Boosting Spells with Possession of Multiple Shards
I think there should be more interplay with shards and their particular spell book. In my opinion, if I have a spell book of a particular element, and two or more shards of that element, that should almost always give the spell a boost. For instance, a sovereign with a fire spell book and 2 fire shards should get a multiplier to the spell, per shard (Ex. Fireball spell with 2 fire shards = (Int/3 fire damage *2), with 3 fire shards it would be (Int/3 fire damage *3). Clearly the multipliers can be tweaked based on beta testing. While the bonus could be easy to figure out for the “damage” or “number” based spells, the concept could be expanded to nearly all the other spell types.
With the recent addition of the non-element spellbooks (combat, enchantments, etc.), the “boost” bonus could still work with the addition of a “neutral” or non-element based shard to the game. Once you claim that “neutral” shard, you would then designate the particular non-element spell book it should correspond to. The “neutral” shard is then changed to reflect the new focus (combat, enchantments, etc.) and it would give bonuses to that spell category accordingly. If that is too complicated, then just make the "neutral" shards apply bonuses to any non-element spell book, but at a lesser multiplier rate.