I totally relate to the opening post! Really. With me being a listener more than an active participant I agree that it is not the quantity of words said that counts, but quality.
I don't know for you, but the lack of skills I tend to notice in myself is not just how much I talk (It could be more), but also how I tend to reply to another opinion or statement. For example, if I say to someone, e.g. "I will fly to the Moon next week", it would seem some people really would care about it, their eyes would become bigger, their mouth would open in surprise. You know, they will show their feelings. It's like they really care.
But when somebody would say this to me, I think my reply would be more passive, like I am not happy for one who will go to space. I will be happy for him/her, just don't have the skills to show this. And maybe someone will think, hey, he thinks only of himself.
It is easier to be quiet when you have a group of people knowing your character (e.g. "(s)he speaks little but when it does it is a joy to listen"). It is harder when you meet other people not knowing "you". They don't know that you can talk even while you don't talk.