i realise something like this isnt likely to be implemented this late in development, even if the developers did like the idea, but here goes anyway 
i think demigod specific items could be used to help balance some of the overpowered abilities by keeping them relativly overpowered but limited by gold and inventory space.
regulus for instance can concievably do well in a game without ever being within visual range of an enemy demigod. so why not have him pay for sniper bolts and mines. you could also have diferent kinds of bolts and mines to add some extra depth. you could have a standard low damage sort of ability without the items at all but then buy the best sort of bolts for the snipe ability to realy see the overpoweredness of it.
also i hear a lot of complaints about the rooks boulder, you could nerf it by making the rook pay for boulders to toss but at the same time add some variety by offering different flavors of boulder. for instance make boulder toss without an item a regular linear damage spell like the qot has but then add a special pricy stun boulder to enable the dreaded boulder/hammer combo.
you could add all sorts of variety and new tactics with all the demigods that way, and balance them out with the gold cost.
just a thought that sounded cool in my head
