unanticipated business customers for my SaaS: how to best capitalize?

I launched Autoresponder for Google Chat a few years ago, originally targeting power-users who have multiple Google accounts. It was my first paid SaaS, and I was more interested in gaining experience than making money.

Over time, I've noticed two customer types I didn't anticipate: owners of small businesses (eg realtors) and employees of large businesses (eg IT support). Both tend to use it for communicating availability to their customers.

How do you think I should adjust the service to better target them? A more expensive business plan seems like a natural next step, but I'm not quite sure how to differentiate it. I also don't have much experience marketing towards business customers.