joined:Aug 1, 2013
My theory is that if you have a clickable link amongst the text that people are reading, they are more likely to click them they would do a simple photograph
You just said a mouthful!
First, text ads do not currently contain anything that looks like a link (unless you actually hover your mouse over them). So, the whole concept of intuitively knowing where to click (from a visitor's perspective) is greatly diminished. This means, you have to get the user's attention with color and get the ad in the path of the user's mouse so when they move over it, something happens to light it up. You do get an underline and a bit of shading on hover so that's something, but the absence of an underlined title has been a problem in my view for some time.
Next, by using both text and image ads, you're driving up CPC. Not just getting pennies for exposures. It helps to understand how the auction works. You're not getting paid what the advertiser bid, you're getting paid what the next-highest bidding advertiser bid. Image ads drive up the "next-highest" amount which is what you'll be paid (regardless of the type of ad). Oh, yes, there's also the pennies earned from ad views (CPM revenue), but the real thing to understand is how the bidding works and how you can drive up the amount you get paid per click when you include both types of ads in a particular ad slot.
And last, since falling off the "text ad only" bandwagon, I'm finding display ads to be quite successful in their own right when added to the mix (particularly rich media ads) so while the old Adsense text ads were king (IMO), I think the playing field is now more level than it was in the not-too-distant-past.