What about the olde tyme voice-overs (BG, P:T) where few key chars had only few voiced sentences? I love this style. You have freedom to write anything. You don't have to be afraid it will be expensive, unrepairable, or even messed by the actor (how many voice-overs are not good? Many). Yet you are able to bring some life and atmosphere to the scene.
"We are all heroes. You and Boo and I. Hamsters and rangers everywhere! Rejoice!" cannot have the same impact if only written ;-)
Agreed, that pretty much what I meant. 5-10% should be voiced like in BG, P:T, IWD, Fallout just story related characters should be voiced just set asmothere. I really love how dialogs in Age of Decadence handled.