I'm in the same boat at the moment, we've raised some seed money and are somewhat in the same boat. In our case, we spent 2-3 weeks of June talking to ~2K of our users on the phone to get some real feedback on how they use the product, what sucks and what else they want to see. At the end of it, we had a pretty solid list of bugfixes and enhancements... but, better yet, we noticed that there were 2-3 specific features that people actually offered to pay for. So, as a final sanity check, I emailed a small sample of those users with a credit card authorization form and asked them to fax it in... I got most of them back (and then shredded them since I don't actually have a way to process them just yet). :)
If your userbase is actively giving you feedback, maybe it's worth spending a little bit of time having in depth conversations to see whether any paid features might emerge?