When we launched Booking X, we initially decided not to add it to the repo. So we try a multitude of things to promote it, including sponsoring a few wordcamps, with out much success. In the end we added the plugin to the WP repo and started to spend $20 a week on Google Ads, over night we saw a vast improvement in weekly downloads. Changing our mindset from developer to marketer is quite a challenge, with a lot of trial and error, but seems to be starting to work.