WoW, 5K per month from Adsense is truly a decent earning here... I'm also wish to achieve this level as well...
Dude I would definitely start finding some other sources of income besides adsense, I was at about 3k/mo on my small web empire and then in about 2 weeks it dropped to about 600/mo for no reason (google slap). I had original content, but it isn't really possible to argue with a website and tell them they messed up since it's like impossible to talk to google.
Well i dont know why people with traffic like that (if he is real of course, which i doubt) would waste time with adsense when you could be making 50x that with affiliate sales.
I have total crap experience with affiliating. I actually don't know how to do it well. I'm sure a day comes when I'm educated on the subject, then I will give it a serious try.
5k per month with adsense is pretty awesome. Especially considering its only 8 sites. 5K PASSIVE INCOME is incredibly awesome dude. Seriously. Are you still even touching those sites?
The thing about affiliate programs is the learning curve and the fat you have to close sales. Adsense is easier and passive. it does'nt require costant work. Personally I'd love to have 5k coming in on autopilot.
I am touching them daily, though no major changes. I improve content slightly, get better images, add new features, and in general try to make the sites as good as possible for what they are. Just because the money are on autopilot doesn't mean I'm lazy or stressed moving on to new things. Now I finally have time to refine the creations.
My average CPC is generally pretty bad, so to earn that much a month I couldn't even begin to imagine how much traffic I'd need!
Niche is as always most important. Don't make a website or blog about your main interest if it isn't paying well. Instead, educate in some well paying niche and get going. It's business after all, not some kind of enjoyable hobby.