Hi Luke, there are a few posts on the blog that might help.
http://www.seomoz.org/blog/tracking-the-roi-of-social-media and http://www.seomoz.org/blog/facebook-twitters-influence-google-search-rankings
I think the consensus is that social shares (by that I mean tweets, likes, facebook shares, +1s) do affect rankings.
If I understand the question correctly, A is the relevant thing here - social signals relating to the pages that you want to rank.
B - If we treat the number/quality of followers etc. as the 'social authority' (who said klout?) of your social media accounts then I believe (don't recall seeing any data) that social shares from high 'social authority' accounts will be more influential for ranking than others.
So, yes, put URLs in your tweets (probably want to use a shortener that gives you some metrics e.g. bit.ly)
Most links in social channels (and I'm thinking of fb and Twitter here), are no follow.
I do wonder, if another way of looking at it might be: I want quality traffic that converts...links can help with that, so can social media (i.e. even if you get no ranking boost from social media, if it brings you the right traffic then that's a good thing right?)