Broadway - 5:48 pm on Mar 30, 2011 (gmt 0)
I serve tens of thousands of page views per day. I don't see the wide variance in CTR that you do.
Yes, I have my days and then other days that are lack luster. I attribute it entirely to the "clickability" of the ads shown.
I've never experimented with the Adwords side but I was under the impression that determining when your ads show could be turned off and on easily, and defined not only by just the day of the week but also by the hour of the day.
I attribute CTR/Income variances to visitor variances (holidays, day of week, etc...) and advertiser variances (as described above and also players with budgets coming into and leaving the market place).
Could it be that the type of ad your typical page attracts is more general rather than specific?
A page about Sony TV's model XYZ would attract very specific on-target ads for model XYZ tv's, whereas a page about TV's in general would attract more general, less interest-specific ads. A type of ad that might be considered to be a "second tier" campaign for a company that only get funded sporadically.
Just some ideas.