Firstly ignore the "Nikon's worst DSLR ever" tag. It is what it is. A camera with good points and bad points. IQ is very good. If you can't get good images from this camera there are other issues in play. One of my favourite articles about this topic is by Thom Hogan. http://www.bythom.com/blame.htm
The D3000 loves nice lenses. I have an Nikkor 80-200/2.8 & Sigma 14/2.8. I am pleased with the results.
For me, the limitations of the D3000 are Poor ISO performance at 800 & over, no mirror up or live view, plus no direct connection grip option and only one programmable button.
Work on your technique & knowledge, buy some good glass, and by then you'll probably have a better idea of what you need in a new body.
Matt ---- "I started on a camel, and I will finish on a camel" Winston Churchill