Send out a unique (unprotected) link per user
I don't know of a single module to do this.  

I would suggest looking at the VBO module (views bulk operations).

You can create an "email" action and customize what gets sent.

From your description I think the biggest barrier you're facing is that users don't want to login,  and you'd like them to just click a link.

To do that you're going to have to roll your own module and likely make use of a menu hook with a callback to a function that processes the link.