Optimize for the sake of optimizing?

I run a couple of websites that gets organic search traffic and has google adsense on them. Unlike most sites, which are littered with ads, my sites only have one ad. The amazing thing is, I can consistently achieve over 10% CTR, and as high as 20% CTR, on my ads.

I always thought this is pretty good, however the other day I got a optimization report from Google, which suggested I put more ads on my sites to increase earnings (I think this only happened because one saturday the CTR dropped to something really small, like 2%, which probably triggered some sort of automatic Google optimization report. I doubt they would have emailed me otherwise….).

But the point is, should I take Google’s advice and put more ads on my sites, or should I stick to my philosophy of creating clean websites? Is keeping a clean, one ad website, the key to my high CTR success? or am I cheating myself out of potential earnings?