Well, in a way your character is always a stark contrast to all the characters anyway regardless of voice, they are weak and worthless and you are the friggin dragon-born!!lol jk
I for one hate fully voiced characters unless it is based in a game with such linearity as Mass Effect, Mass Effect was quite linear as the Quests are all pre-set and doesn't change throughout the main quest arc, whereas Skyrim is a much bigger, non-linear game where you have a lot more side-quests plus the radiant story added in to Skyrim, you just can't add a voice to TES characters unfortunately, but in a way you do add a voice in a sense as you imagine the voice of the person and how they would be expressing in game, as it is your character not "Hawke" or "Shepard" it who you want, and in a sense the person you create would have the personality of you, therefore you are in a sense the voice, and you are the person that decides on what to say and how you feel they would express them, it is the whole point of Role-playing, to feel that you are the character, not a mere-bystander retelling events...
Well... to be fair, the game gives you a preset list of choices as to what one can say. It's not like you are in COMPLETE control over your personality as it is right now. As far as imagining my voice, I don't do that. I'm concentrating more on what's being said and following the story than imagining even my own voice in the role. So I would find it much more immersive and interesting if my character was fully voiced. There is no reason I can see, for me at least, that it can't be done even in a fully open world game like the Elder Scrolls and all the choices that come with it, because to me it adds to immersion/roleplay. It does not detract unless it's done badly, which I wouldn't expect to happen here. However, as already agreed upon, it comes down to preference and alas, the overwhelming majority seems to disagree with my opinion, including I guess Bethesda.
As for what the OP is suggesting, which is just to modulate the pitch of the grunts and things for the player character (not fully voicing as I've suggested), I'm pretty sure that all they have to do is take the voices that are currently being used for the player character and modulate the pitch using the same kinds of tech they use in music videos and movies and such. I don't think that necessarily means you'll sound like a robot either, but I wouldn't know that for sure. I'm also not sure it would take a lot of memory (it might), but all it would be doing is modulating the pitch of what's already there based on the level on the scale you chose. They wouldn't have to record a crap load of extra voices for the character. That is what I think the OP is suggesting which people seem to be missing as far as I can tell.