Having the option to use Vigor in some spells

how worse is the "level scaling" you mention ("It also makes physical abilites scale much worse with level, obviously.")? How much stronger would an attack made by a level 50 character with the same vigor and battle power than one of level 10?

Vigor and Battle Power has very little effect compared to Level in vanilla. Since one of the terms in the formula is Level * Level, you can see that damage scales pretty much quadratically, while Battle Power and Vigor don't have a big effect. In other words, even a weak weapon or physical ability will do a lot of damage if your level is high.

The magical damage formula is much more egalitarian with regards to stats; damage scales linearly with each stat. Even on a low level, a character with high magic can do a lot of damage with a strong spell. In other words, Magic and Spell Power have a much bigger effect. And, with my hack, Vigor and Battle Power do as well.

From Terii's algorithms FAQ:

Code:

For magical attacks made by characters:
Damage = Spell Power * 4 + (Level * Magic Power * Spell Power / 32)

For magical attacks made by monsters:
Damage = Spell Power * 4 + (Level * (Magic Power * 3/2) * Spell Power / 32)

For physical attacks made by characters:
Damage = Battle Power + ((Level * Level * (Battle Power + Vigor * 2)) / 256) * 3 / 2 

For physical attacks made by monsters:
Damage = Level * Level * (Battle Power * 4 + Vigor) / 256

My hack makes both characters and monsters use the same formula for damage:

Code:

Magical Damage = Spell Power * 4 + (Level * Magic * Spell Power / 32)
Physical Damage = Battle Power * 4 + (Level * Vigor * Battle Power / 32)

Note that in vanilla, monster Vigor was randomly distributed between 56..63. With my hack, Monsters can have between 17 and 96 Vigor depending on their Max HP (it randomly varies a little bit).