Jade: 

"Q: What is PreCheck?

A: The program allows previously vetted fliers to use special lanes at the checkpoint. Shoes, belts and light jackets stay on. Laptops and liquids stay in bags. And these fliers go through standard metal detectors rather than the explosive-detecting full-body scanners most pass through."  "

This info is from the TSA website.  It seems to indicate that you are correct.  Only when you finally reach the "check-in" point do you gain anything.  At that time you're directed to that "fast lane".  It seems you still get to stand in that long queue waiting to reach that checkpoint.  

Don't be bothered by the trolls from 4:20 regarding this issue.

I still am not sure on the First Class question.  I know that they avoid the long lones at the airline desks.  I'm not sure if they get to also "jump the queue" and avoid those lines waiting to reach the TSA check-in point.  If they do, that's really bogus in my opinion.  thanks and regards, Gary