I think instead, Songhai should have a combo enabler that benefits from using low cost spells.
Rough example:
Phoenix oracle
4 mana 4/2 Arcanyst
Whenever you cast a spell that costs 2 or less, draw a card.
This would help reward players who play lie cost spells while also supporting cards like Mana vortex. Of course, mana cost and stats can be changed, but the general concept is there.
EDIT: on second thought, I think a neutral minion would be better to provide viability in all faction low cost spells.
Mystic Oracle
4 mana 3/3
Whenever you cast a spell (this turn?) that cost 1 or less, draw a card



AD is a +1 with 2 minions active, and scales up from there. HE is a +2 and one of the spells can be replaced for a minion. Koan is what it is. Not to mention that Xho and Fox generate lots of cards on their own.