You can’t really know how your tunes are doing before you get first Content ID report. As Flumen said, the youtube popularity is totally different kind of beast than stock music licence sales. You might have 200 videos but still get almost nothing for some tune and have only 1-2 videos for another tune and get 1000$ for it. It all depends on so many factors.
I don’t want to mention exact sums, but for me it has been very good decision I don’t regret.