Another way of looking at it. If a user never/rarely clicks on an ad, and happens to click on an ad, it may be because -
- The regular SERPs weren't good enough that he/she chose to click an ad instead. (I rarely click an ad, and there are few rare occasions when I had to look at the ads to get the site I wanted)
- The ad creative (Title/Description were just what the user was looking for and induced him/her into clicking, vis-a-vis not so relevant regular SERPs)
I guess, it is quite assumptive to generalise a user who never clicks an ad and if he/she clicks then that is a "poor prospect"