Suggestion: Every shard you have increases your rate of mana rejuvenation. 

Suggestion: Every shard you have adds to a pool of mana your Sovereign and/or Champions can also draw from instead of just their own.

Suggestion: Must have a shard for your Sovereign to escape to from a death blow in battle

Suggestion: Shards add to the magic resistance of every unit in your domain

Suggestion: Shards greatly reduce the amount of mana needed to maintain spells of their particular domain.  This would allow anyone to cast the spells but maintaining them (buffs) would be more painful without the shards.

That's all I have for now.