It's important to look at Twitter as a way to engage with your fans and get your content out there rather than solely as a way to increase your rankings. If you're not there to interact with people, you'll find that they get uninterested quickly. The same goes for Facebook, Google+, etc.
I love the idea that Aran mentioned about having a Youtube channel. You can do a lot with that and even could post the videos on your site and tweet those links. One of the greatest things I've found though is to simply ask! Ask your Twitter followers what they'd like to see from you on Twitter. People LOVE giving their opinions so I'm sure you'll get some feedback. You could try that on Facebook and Google+ as well.
The idea really is to get a group of fans who are interested in what you're writing about or posting on your site as well. Maybe it's tour dates, or posts about your concerts, but something that gets people interested enough to tweet and retweet.
Hope this helps a bit!
Jen
One tool I can think of that I think is PC only is Xenu linksleuth. Otherwise I've been able to find everything I need on the mac.