I agree with your statement about favorites. I think, if they promoted them, they would be a great way to help rank content. I think this, combined with retweets could really help bubble stuff up to the surface.

Part of the issue with retweets is that the whole network will become more noisy and people will have to get used to that, I think this is partly a mistake. It could be fixed by allowing users to favorite cool things and retweet things they REALLY wanted to surface.