The question is: would you like to upgrade your equipment or improve you photographs?

If it’s the latter, then the next question is: how? Most of the times, the amateur concern about resolution, vignetting, distortion and so on is nonsense. As you have pointed out, a camera doesn’t make photographs, photographers do.

You already have an excellent gear, stretch it to the limit. Try to reproduce pictures from photographers you like, take part in contests, travel, make illustrated reports as if you were working for a magazine (even with a deadline). There are many ways you can push yourself to improve your pictures and also develop your own criteria about what it’s a good picture. Then nobody but you will be able to know if you need another camera or lens.