The damage scaling for magical characters (mages and guardians) is 20% of their magical power. Physical gods get 100% scaling.
the formula is: (Base Damage + (Base Damage per lvl × God's lvl)) + (100% of Physical Power OR 20% of Magical Power)
so as an example. Anubis's base damage at lvl 1 is 35 and every level he gains 1.5. If he got 100 magical power, the formula becomes (35+(1.5*1)) + (100*.2)) = 56.5.
Anubis will deal 56 damage to the enemy if they have 0 protections.
Yes, building magical power is not only good for your skills, but your basic attacks as well.
source and more info here
I missed the part of your question about enhancing basic attacks. Yes there are a handful of items that give you an extra oomf on your basic attack. they are:
- Telkhines Ring gives extra 40 magical damage for each basic attack (so it just adds 40 to that formula above)
- Polynomicon after using an ability, you gain an extra 50% magical power damage on your next basic attack.