I don't know much about Esperanto, but if I ever find time to learn I would happily use this site. It appears to be well moderated and filled with quality content. In my opinion that makes the site useful even if visitors and questions per day are not as high as you would like.
As a moderator of another SE site launched close to the same time as yours, I also monitor these statistics. Your answers per question and answer % is high. This tells me that your SE community is comprised of many experts. Try to think about ways to attract more beginners likely to ask questions.
I have found some success in regularly posting links to SE content on Reddit (with the support of moderators there) when relevant. Try to think about why a newcomer would choose to ask a question on SE instead of (or in addition to) other available Esperanto learning sites. Maybe a large percentage of potential users are not yet familiar with SE and its unique advantages.
We have no official relationship but because of our shared vocabulary there are some Monero users interested in Esperanto. I speak only on behalf of myself but I am more than happy to hear ideas that could help cross promote our SE sites.