I often post bounties and posted about it a couple of times and I've had a few enquires on the use of it and got some steemians to use them. I even placed a bounty on someone else's post just because I liked it and hoped it would get her more responses and answers
The people who are using bounties are the ones who are now familiar with it so why not let the next challenge be for outreach. Ask users to find other users posts and place a bounty on someone elses post and share that post. That way it can reach users you don't normally reach and it creates extra interest
Also when setting up a bounty now that steemit can filter resteems, it would be great if bounties were resteemed by the @steem-bounty account and use that as an additional marketing tool to get the word out there and get more people interested and involved.
Finally since the https://steem-bounty.com/ website is running Google Tag manager you could easily add facebook, Twitter and Google Remarketing pixels so users who have visited the site can be tracked and advertised to, to bring them back to the site as well as using that data to model audiences that would potentially be interested based on their matching traits in user behaviour