Depends on your landscaping and where you put it. If it will be close to the house and you have that perfectly manicured yard then, insay it demands a paint job. If its out in the yard and will have wild flowers growing all under it or something like that, I'd leave it.
My opinion aligns with this.

The overall design and the aesthetic you are trying to create will dictate.
Personally I love old rusty implements and trucks with flowering vines and wildflowers.