I've heard a lot of people say fully voiced dialogue is one of the worst things to happen to RPGs, and I agree with them completely.
Far less content, far less options, far less left to the player's imagination, and far less mod friendly... all for what? A slight boost in immersion that gets undermined anyway by re-used voice actors and NPCs spouting the same sentences over and over again.
I say go back to the Morrowind approach. Written dialogue for the most part, with voice acting for greetings and small portions of ambient dialogue when walking through the world for immersion.