I'm open to discussing this, but I'd like to address one thing first: what kind of interaction do we want to encourage here?
If you like something, you can star it and move on. If you LOVE something, so much so that you want to share it with people who follow you, surely you…
I honestly don't see how a social network can survive without retweets. They're just not going to get the critical mass. There needs to be an "amplify" gesture and quote ain't it.