Banners and such are PUSH for a customer, he didn't do any action to call the stuff in his eyesight. Coupons are just tingling at the side and if a curiosity makes a user to click on it, this generates PULL effect and he is more likely to engage with a coupon. Or in the other words, this means coupons are a holy grail of advertising :D
They won't. As long there are good deals on coupons, ppl will want to uncover them.
I even beleive that a site with a good marketing team could get rid of banners and use only coupons, which would kindly benefit the site visual complexity.
CTR for badges was like 8% with all the timing and randomness tweaks. Since coupons are not used to drive traffic to other sites we also measured newsletter signup and the engagement was mindboggling 3.5%