to trek across the universe to visit the first planet?

While I can't speak for NASA's programmes, one thing is certain: you massively underestimate the vast distances in question.

Say one of the planets of the quite nearby Gliese planetary system turns out to support human life. This system is "just" 20 light years away. If we had the funds to build a probably massive space ship (we don't) , and the technology to accelerate (and decelerate) it to (from) 0.25 c (we don't), but let's asume we do: the journey would easily take close to 100 standard Earth years - and that's just one way. Forget the "just visiting" part ;)

You'll need people willing to sacrifice not only their entire life, but also their children's and great-children's just to be sure, that the latter's kids eventually arrive there.

How do you organizea balanced reproduction without inbreeding, how do you feed the travelers? Once you leave our solar System, there's absolutely no resources you can collect from outside. Everything aboard will become incredibly scarce and valuable.

Not to mention communication with Earth. Midway you'll have a delay of 10 years until your message from the space ship arrives at your former home, and more than 10 years until an answer arrives back to you.