4 few years ago a friend and I made www.turntubelist.com to scratch a personal itch. We've never tried to advertise it or push it anywhere but overtime the users slowly climbed from 50 hits a day, to 100, to 150... but then 6 months ago something happened. I dunno what, but it happened from Brazil, and then Japan then kind of everywhere - 6000+ visits a day for weeks. It's settled down now - about 1500 visits a day... but the people who use it have a REALLY long average-time-on-site: 26 minutes, according to Google Analytics.
There's no ads up there at the moment, which would be the obvious thing - but because it's all client-side it would be hard(er) to get relevant ads (like for the songs the user is searching for etc).
Anyhooo.... What would you do with it?
What you do have is validation that you have something going on there, now you need to analyze what that something is and if there is a way to get it to grow to a substantial multiple of what you have today.
So, what I would do with it is analyze the crap out of it to see if it has (autonomous) potential for further growth.
You also need to figure out why it dropped again.