I like that
I agree with leaving it as is. If you needed to freshen it up, you could acid wash it, but that may stain your primer.
I am also curious as to the thickness and what mods you may have done to accomodate the planks. I am familar with the aluminum planking on semi trailers, but I had not thought of bleachers. The semi trailer planking is about 1-1.25" thick.