Great Work!
Only 2 things:
I agree with Cheiromancer, +4 per +1 enhancement bonus past +5 is ok, At 21th level it would be very usefull!
And the energy seed must have a base damage of 20d6 to be usefull, 18d6 of energy damage at 21th level is useless, 28d6 starts to look like a epic spell.