In my opinion,I would say twitter will be only useful if you have a certain reputation and credibility in the online field. Think about it, it takes seconds to create an account and there are millions of people posting their tweets. There must be something that distinguishes between you and the other fellow people. Social media marketing will be the best if you have a reputation
You said you can't keep up with it... are you overwhelmed by the number of people sending tweets to you? are you dissatisfied with your recent results or experience with it? Well, you probably already know about different tools to schedule your tweets. there's one in particular in which you put in a list of tweets to be spread throughout the day so you don't overwhelm followers. if you've got 9,000 followers and can't get many leads I would think most of your followers aren't quality.
Using Twitter certianly doesn't hurt. I get traffic from Twitter. It doesn't take long to send a tweet.
Obviously twitter is a powerful social media tool when we do have a great followers base and when we do use it in a right and effective way. I would recommend you to link your twitter account with facebook, so that your tweets can have more exposure than it having alone within twitter.