I just don't see the reasoning behind making Spears a Dex weapon to begin with. It's hard to imagine a stealthy rogue-type carrying around a huge spear....
In any case, I'm all for consistency. I have a complicated proposal which everyone might dislike but here is the idea:
Ranged attacks:
If ranged attack is physical (bows, throwing knife): Dex scales dmg.
If ranged attack is magical (elemental dmg on bows, wands, staff of magus skill): Int scales magic dmg and Dex scales physical dmg.
Melee attacks:
If melee attack is physical (every melee weapon except staff): Str scales dmg.
If melee attack is magical (any elemental dmg melee weapon, staff): Int scales magic dmg, Str scales physical dmg.
In this model the dmg scaling is based on the particular type of damage, regardless of weapon type.
In addition, backstab (if it is to be kept as a Talent choice) should only apply bonuses to physical dmg, and should apply only to melee attacks with Daggers, Swords, and Spears (i.e. weapons that you can actually stab with).
I see the point about hitting someone in the back of the head with a mace, etc, and this makes sense. The only thing that bothers me about that is the "stab" part of backstab. Maybe if they got rid of the backstab talent altogether, then all attacks from behind could get some bonus as you guys were saying. That would make sense, too.
