Duane, 300 dpi is the setting I used when I scanned this color image from paper. Isn't this what you are referring to as "native"? Doesn;t it seem readable?
Also, isn't 300 dpi an arbitrary standard? I am thinking that the important feature we are seeking is whether the image is clear. I can guess that highly-detailed maps need this native resolution. But a simple 5K might be just fine - in color or B&W at something less.
My experience with image manipulation is that sufficient experimentation usually gives you what you want - where there's a will there's a way...(smile)