In my experience bare GMK ABS doesn’t really attract that much dirt and whatnot, even some of the lighter colors. At least not as much as either PBT or a GMK set covered with clear coat, which does seem to attract dirt over time noticeably.
Will shine. It’s an inevitability that just takes longer for some than others to occur. I’m unfortunately particularly bad about shining GMK and can get some mirror spots on a spacebar in just a few months, part of the reason I’m starting to move away from GMK.