I think the k3 is still easily worth it, if you can get one for under 500 with a 3-6 month warranty. Keh has a grade comparison table if you're interested, make sure to view it in desktop mode to see the correspondence to others
Grading System at KEH Camera
I have the k3ii, I am perfectly happy with the sensor, and my shooting includes low light such as concerts (I've shot at 12800 and loved the photos, though print sizes would be limited, for a newspaper color print they were fine). I shoot raw though, I think the jpeg engine leaves a lot to be desired at such high iso. It's a high grade dependable body, just be aware of what features the newer kp has and if you don't see them worth the extra money, why not?