The 8320 is a pretty damn good CPU. As for upgrading being worth it, I would say it depends entirely on what you want to get out of your PC.
If you want to game you'll almost be guaranteed a higher FPS (assuming no GPU bottleneck) going with the 4770K, but if you use the computer to render things, encode, or well multi-threaded stuff, then I would wait for a more significant improvement before buying a new CPU/MOBO. Maybe 1-2 generations past this.
Assuming Haswell-E is going to be the same as a 6-core version of the Haswell i7, expect the same performance increase you'd see from Sandy to Sandy-E. If you're gaming, it won't be noticed. If you're encoding videos expect a reliable 50% boost from the quads, and in that case it would most likely be worth an upgrade from the 8320 if it's not too much for your budget.
Originally Posted by PontiacGTX
At higher resolution the less is the cpu importance,
This is so untrue.
The importance of a CPU can only rise with a higher resolution, it never
become less important.
Resolution is almost 100% bound to the GPU performance, with the exception of UI elements and some other insignificant things. The CPU is always very important, even if you're gaming at 800x600.
It doesn't matter if you run the game at 16M x 9M resolution or 1920 x 1080 resolution, if the scene itself has the same complexity, the CPU load will usually not change a bit. 3D Meshes are scalable, so all the CPU has to do is really load the mesh to the GPU, and from there it does it's own thing.