Depends on ur need. If the camera body i'm aiming for is a D7000, I would not downgrade to a D3100 to get better lens. I will miss out lots of needed features becos of that. But that's just me, it would be diff for your case.
I personally feel that unless you are printing images at its 100% size, you won't actually need "better lens", unless you need something that the current is unable to deliver. and IMO, better skills and different perspective will be more useful in the long run.
*currently I'm not a believer of better body/lens = better shots*