First off, here's the text of the Blood Intensity bloodline mutation:
This ability replaces the sorcerer's 3rd-level bloodline power or the bloodrager's 8th-level bloodline power.
(Source)
On the face of it, this seems pretty straightforward. If a 15th level Sorcerer with 20 Charisma uses Blood Intensity with a Fireball, it will deal 15d6 damage as a 3rd level spell. This is the same damage as an Intensified Fireball, but it is more limited in uses per day in exchange for not requiring a higher level spell slot or having the longer cast time of spontaneously applying metamagic.
However, since the maximum damage increase scales based on your Charisma, rather than being set at 5 levels worth, this means that a 20th level Sorcerer with 30 Charisma can cast a Fireball that deals 20d6 damage.
Is that all correct so far?
Here's where I really start questioning things. Each successful hit with Battering Blast deals 1d6 damage per two caster levels, up to a maximum of 5d6. Assuming an appropriate caster level, an Intensified Battering Blast would deal 7d6 per hit. "An intensified spell increases the maximum number of damage dice by 5 levels." this is essentially reduces to 4 in this case, since the fifth level is not enough to hit the next scaling breakpoint.
Blood Intensity, however, states that "you can increase its maximum number of damage dice by an amount equal to your Strength or Charisma modifier". There's no mention of level here; it increases the maximum number of damage dice directly. Does this mean that our Sorcerer with 30 Charisma can cast a Battering Blast that deals 15d6 per hit, assuming a sufficiently high caster level?
A level 20 Sorcerer has a starting caster level of 20. The feats Bloodmage Initiate, Varisian Tattoo, and Spell Specialization can increase the effective caster level by 4, and all of that can be doubled via Spell Perfection. Add in an Orange Ioun Stone and the Gifted Adept trait to hit a caster level of 30. On top of all that, add the Orc bloodline and Blood Havoc for a total of +2 damage per die.
Suddenly, we have a Sorcerer that can cast a 3rd level spell that can hit up to 6 times for 15d6+30 each. Add Empower and Maximize Spell to bring it up to 6 hits for ((15d6+30)/2)+120 each as a 5th level spell (since we're using Spell Perfection anyway). Assuming every blast hits, that's an average of 967.5 force damage in a casting, and we can throw in a Quickened Empowered Battering Blast for another 742.5 average damage, totaling to 1710 average damage in a single turn at the cost of two 5th level slots and two uses of Blood Intensity. That doesn't even account for the chance of a critical hit somewhere in there.
Ouch.
Well, it's not just battering blast, though there seems to be fewer 1dX per two levels spells on the Sorcerer list than the Cleric list. Vampiric touch would work much the same, but it caps out at 10d6 normally, so you can't see any benefit with it until your caster level gets to 22.
That is an interesting observation about empower vs maximize in this case.