2nd k7 or new kr?
You already have a D5000 which is good at high ISO. I would try the K-7 because its a different league of usability. Although not great High ISO, but still usable at 1600 and 3200 sometimes. the D5000 is around a stop better IMO at higher ISO.
I'm thinking to invest to high grade lens and googled around and found out pentax system produce great colour and neutral (portrait and landscape) especially from limited lens. Most of them came out from k20d. But i prefer latest body with more function and feature and weather seal body. 2nd hand K7 body same price with new Kr here.