In my opinion, the crowns look fine and perfectly normal, especially on the first picture. In the light it might look a little sparse but definitely nothing out of the ordinary. And the fact that it has been stable for 13 years is a great sign as well.
If you're concerned about keeping what's there, then you can try Rogaine. But I wouldn't do so unless you start noticing things getting worse. From what I understand, if you use Rogaine you're basically dependent on it for the rest of your life.
I'm no professional, another 'newb' worried about my own hair as well with very much the same issue as you - no receding, just what I thought was a strange looking crown. I went to see a dermatologist and this is more or less what they told me.
