You could try to somehow monetize your data that describes who is paying for what services. Even if it's just blog posts with general graphs (like OkCupid) it could at least help your brand. For instance, ADP's employment statistics are as closely watched as government statistics by some people on wall st.

I wouldn't necessarily encourage you to directly sell detailed info about your users to marketers as it may very well annoy your customers, although there is probably a market for it.

At the very least, bringing in a consultant to do some data mining to find patterns that correlate to actual revenue may help you with all your other concerns.

Once you feel confident you know who is really spending money and why, an inside sales person to cultivate a list of potential customers is probably fairly cheap and may lead to a real uptick in sales. You seem uniquely situated to hire someone like that through your own service.

While writing this comment, I keep being reminded of Groupon. The last time they raised an obscene amount of money, the investors kept talking about (1) their sales army that had a relationship with thousands and thousands of small businesses and (2) sales data for all those businesses. You could read up on them to see if you get any ideas.