I vote for keeping the older camera, getting better glass.
Cameras lose value quicker, glass prices stay relatively stable. If you buy the lens and are still unhappy with your quality, then I'd say invest your money in a new body (unless you really NEED the features like WR, higher MP, and focus-peaking that the K-30 offers right now). Most likely you won't even notice a huge difference in your casual every-day shooting between a K-r and K-30. The best photographers can make even the crappiest of cameras perform like champs.