If you could persuade your existing visitors to install the Alexa toolbar, then that would boost your Alexa ranking without increasing your traffic. In fact, installing the toolbar yourself and visiting your site more often would help to a degree. I don't think Alexa ranking is particularly important, though. Too few people have the toolbar installed for it to be reliable, it's open to manipulation, and it tends to favour techy sites whose visitors are more likely to have the toolbar installed than other users.