Honestly AdSense eCPM is through the roof since they started doing retargeting. Its now much more about your demographics than your content.

For example, back in the day, a forum for a Warcraft Guild would have triggered "Buy Gold Now" ads which paid pennies per click. Now ads are targeted to the user and know the user's search history, so the ads can be much more relevant. Given that Warcraft players are often rich techies, suddenly the ads being shown have a much higher CPC.

In short: sites that 3 years ago would have paid pennies per click are paying dollars per click on AdSense. Its kind of insane. If you wrote them off before I'd consider taking another look.