I think there should be limits on the spellcasting abilities of your Sov if you are not putting points in his intelligence...  A 8 INT sov should not be able to cast 30 INT spells... 

Perhaps some kind of percentage...  ex.  A 22 INT spell x 50%? so a Sov needs at least an 11INT?  I think it should be closer to 65% myself..

Though some of the ridiculous INT spells which are clearly designed to limit them to Sov only will need to be adjust so that they can still be cast...

2nd idea..

Weapons and armor usage should be tied to STR and/or DEX...  ex..  using a massive warhammer should not be possible by a 8 STR sov or champion.. etc..

Just my thoughts...