I'd like to point out something I discovered while I was playing with my battle mage. If you equip a one handed melee weapon in your primary hand and a wand in your secondary hand you get the stat bonuses from both weapons but you will only use the melee weapon when attacking, which still only costs 1 AP (although the game bugs when you do this and tells you that it will cost 0AP to attack). I have no idea if this gives you the skill bonuses for single hand or dual wield.
I think I'd still prefer it if single handed was buffed somehow though. I really liked the look of my battle mage fighting with just a one-handed sword and I imagine it would look a bit silly for a stealthy rogue to have a dagger in one hand and a wand in the other. Making the AP cost of warfare skills dependent on the AP cost of a regular attack might be a good change. Another cool change could be some sort of "Duelist" talent which doubles the stat bonuses from your primary weapon if your off hand is empty.
