At the moment we are cold-calling, which is working wonders, but its very slow and time consuming. Requires calling, getting to the right person, then maybe a couple calls, then bingo! Then an email in response. Looking at cost-effective options. How can we be more targeted. Email marketing is an option, but I don't want to just send a bulk of unsolicited emails (done it before, mail chimp etc..., need to add some form of value, understand our different segments). Trying to avoid to just send newsletters... what options could we try?
Names and contact details are great assets, and cold-calling as you say can be effective.
Now diversify your efforts. Cold-calling is about sales, it is a direct fairly yes/no conversation.
At the same time use other channels to educate your audience. What is happening in your industry that can impact your clients? What are alternatives to their problems they may not have considered? What news should they be aware of?
Use content to engage in a different way and start on-going conversations, in addition to the yes/no ones.