New camera, or a new lens? Help...

Stephen_H wrote:

"Which will give me the greatest benefit... a new body, or a new lens?"

Note: My photography needs are broad from family shots at birthdays, to pack photography at the office. I'm not a professional so I don't earn anything from my camera. It's a hobby & a tool that my wife largely sees as a luxury with all the cellphones floating around.

Actually, either would help. Which would help the most depends.

New camera: when I upgraded from my original K-30 to the K-3, my low-light capability improved tremendously. The plastic fantastics (35 and 50mm) specifically went from almost unbearable hunting to fast focusing. I'd expect the same 'wow' experience for you, since the K-70 and KP are another generation again, and much more capable at the high-ISO end.

New lens: I agree with the endorsement of the Sigma 17-50mm F/2.8. It's a good, fast-focusing lens for me even in low light. It is a bit big, though, and I can't say how it does on the K-50.

Either way, however, you're still stuck with outdated focusing capabilities or a mediocre-at-best lens. If you can, you might try stretching the budget to a k-70 or KP kitted with the Pentax 18-135mm. IME it's a better lens than the 18-55. Either combo can be had from Amazon ($796 and $980 respectively).

If you really don't want to spring for both camera and body, though, then the surest bet, FMPOV, is the camera upgrade. I'd expect even the 18-55mm to perform better on a camera that will let you boost ISO higher, and Pentax body AF has improved over time.