I've been using retweet exchange services and have noticed some upward movement for SERPs to two of my sites without doing any other link building. Now I'm not saying you'll get to the top of Google with retweets, but I think it's valuable to have something extra in the arsenal to help with giving your site a boost. I haven't really noticed much traffic coming from the retweets though that's to be expected as most people using the exchange services either have nonreal followers or people who don't care about what they have to say.
Anyway, you may want to experiment to see what it does for you. I created an account before using these sites and used twiends to get enough followers, plus used hashtags like #followerback #instantfollow etc as I don't want to spam my followers from my MS when earning credits. The sites I've been using:
http://easyretweet.com/
http://retweet.it/
http://adretweet.com
http://justretweet.com
Anyway, you may want to experiment to see what it does for you. I created an account before using these sites and used twiends to get enough followers, plus used hashtags like #followerback #instantfollow etc as I don't want to spam my followers from my MS when earning credits. The sites I've been using:
http://easyretweet.com/
http://retweet.it/
http://adretweet.com
http://justretweet.com