Here’s my cart with a very basic noise dust/grunge effect using a method similar to Kent’s Z Normal.
It took maybe 5 minutes to set up? The grunge is only on my local copy and not the Google Drive. I’d only add it if might added to the scene or not. But as you can see below, the grunge is only really visible from close up.

Rendered View, Close up.

Rendered View, Main Camera.
As you can see any subtle accent like grunge/mud wouldn’t add anything to the final composition.