Hi Daniel_Santos welcome to the forum
I am not a lurker. But when I read a post in a topic I haven’t posted in that “answers a question”, I Like 
it. I can’t vouch for how valuable a metric it would be, but it should be easy enough to use the Data Explorer plugin to find the number of members that haven’t made any posts but have Liked.
Personally, I find exit pop ups annoying. I have no problem with “was this helpful? yes/no” inputs and sometimes I actually use them.