This grungy vignette effect was created using the ‘mezzotint’ effect from the Effect>Pixelate menu. To summarize, you start off by creating a radial gradient, from dark on the outside to lighter on the inside. Then expand it and apply the image trace.
It’s a simple way to achieve complex effects using Adobe Illustrator. You can also experiment by using the linear gradient effect and try out some of the other mezzotint options, such as lines and strokes.
You can also change the final outcome when using the image trace. Try adjusting some of the image trace settings, such as the ‘threshold or paths. Remember to expand after you’ve finished with the image trace. Then select all of the white areas and delete, leaving just the black.