I do get retweeted, and a retweeter the other day got my book recommendation from @Amazon, which is cool.
I do use twitter for promotion, but the best way (for me) is through the judicious use of the hashtags and @s so new people can stumble upon my books. For instance, I @ to free book tweeters, so they then can spread the word to their followers.
Personally, I don't think your followers on twitter are the reason for tweeting if you are using it to promote your books or brand. Reaching new people is my goal so I don't worry if someone unfollows. Frankly, if they have less than a thousand following them, my tweets in their newsfeed would be annoying and I expected them to unfollow.
I only send out two to four promo tweets a day (I don't go on everyday), but I retweet, reply, and post interesting stuff too.