Not only is 're-targeting' immensely useful, it absolutely increases conversions.
Targeting in general helps quite a lot.
Ad targeting is the opposite of evil, it actually increases relevance by a significant degree, and increases market efficiency, wherein surpluses go to both sides. There's a huge market for products and services out there and it's getting harder to connect individuals and products on the long tail.
Without tracking - the big winners will be the mega-brands that can run wide ad runs to most of the nation. It'll be cheaper to just tell everyone about McDonald's and impossible for the new snowboarding company to tell you about their new gear.