Dual-wielding is hard because it adds another style to balance. It has to be given something to make it not clearly superior to single-handed (or worse, single-handed with shield, which has two different abilities you need to spend points on).
The AP system can help with this, I suppose. Simply add the AP costs of the weapons together and you can attack with each weapon, but each attack costs much more, which means that on any given turn, you can move, or you an attack, but not both (or you can skip a turn to save the AP so you can do both next turn).
Daggers, though, might be a bit powerful when dual-wielded.
I bought a Push Dagger requiring Level 5, and it worked very well indeed, even on the undead. The low AP cost plus high critical chance plus backstabbing works well. One fun strategy is to hold the rogue back for a turn or two to max out their AP, then have some teleport them behind enemy lines. The rogue might die, but can take out two or three enemies. I did 220 damage in one turn in 12 attacks, and I missed once, and 3 others were for normal damage not backstabs.
Since a dagger costs 2 AP to use, two would cost 4, but since the dagger animation plays twice, you still get the same number of attacks, dual wielding or no.
