Parked pages are good for sites that are getting a good amount of type-in traffic and you want to sell the name to end user (meanwhile also earn parking revenue). Its not really a monetization technique in my opinion. Creating meaningful website and then putting up ads is always way to go. It can maximize the earning potential especially for the domains that get type in traffic.
Although some clicks might be made on ads displayed on parked domains, but by checking out the options being used by professionals and expert marketers, you will notice that such minimum cash amounts are far from real financial potentials of the established portals and projects. Some people are earning hundreds or even thousands of dollars a month because of Google AdSense units published on their full-fledged websites, enjoying top Google ranks and receiving lots of hits plus page views a day.
You can check the traffic on your site and conversions after performing SEO activities rather than checking what have done for the promotion of your website. You can check from Google analytic. You can also update your monthly report for keywords.
Why not just put something simple on there, like a wordpress or joomla blog or something simple instead of just parking the pages. I think you will have a better shot at gaining money through your adsense, while at the same time helping your domains increase their rank.
Create a webpage and then placing adsense on it rather than using googles own parked page would be better choice. It will offer your more admin power to invite more and more traffic with increasing SERP.