It would be interesting to see what mobile devices are being used, and out of these devices what ones are clicking on the ad words.
I say this because a website displayed on an iPad or PlayBook wouldn't and work a lot better compared to a site displayed on an iPhone or HTC Desire (for example). Personally, when I look at sites on my PlayBook, I tend to use the desktop version of the site and not the mobile version. a 7" or 10" screen is better suited to displaying non-mobile sites.
Compare this to me viewing sites on my Samsung Omnia 7, well normal sites are just awful. So I tend to go for the mobile version of the site.
If, in your case, most of your revenue is coming from people using Tablet PC's then I wouldn't change a thing. Obviously there are other things to consider such as time on the site etc, but if it isn't broke why fix it? However, if revenue isn't coming from the users of mobile/smartphone devices, then obviously change the layout to something responsive.