I'd like to see some staves that just amplify your spell damage and/or reduce spell cost. Some of them could require two hands to use, with secondary attack being a melee block, and primary attack doing roughly the same thing that dual casting would (though thinking about it, the only two handed staff casting animation I've seen was in Dragon Age 2, those would take some serious work.) I still think the current staffs have their place, especially at lower levels when magicka management is more of an issue and your spell repertoire is limited.
Exactly.
Maybe they could be equipped both one handed and two handed, like current spells.
Provide bonuses to whatever spell is equipped in the hands (damage/duration/regen/cost/aoe, etc...). If held two handed, then they should be better than dual casting a single spell from the hands. If one handed, the staff should be better than single casting the spell from that hand.
With no spell equipped you should be able to swing them as a blunt weapon at the very least (and block!)
There needs to be the incentive to use them over bare hands, so acting as a conduit to amplify the power would make using them more attractive.