I'd definitely like to see him given a speaking role-- there are ways of conducting his speech without infringing upon his open personality. Link shows what I'd call reactionary expression-- the script is written in such a that Link's thought and emotion, while appearing independent, is actually the product of what's going on around him; the script is written to only procure one emotion from the player, and Link acts as a funnel through which that emotion is conveyed, relating the player to him. Words coming out of Link's mouth wouldn't change this, he'd still react in the way he currently does.
In terms of giving Link character development-- we've seen some of this, particularly in the 3d (and DS) games, but not to a great extent. I don't think Link should be given an independent personality-- I think he should still relate to the player, and giving him a separate personality would ruin that dynamic. However, as long as the development carries through to, and is felt by, the player, I think it'd be an excellent idea to incorporate it.