A 2D sprite or a actual image has been drawn to the resolution of the original hardware and cannot be improved other than overlaying a shader as stated, so don't expect any huge improvements, the games are old, made in low resolution, and designed to run on CRT monitors, not the flatscreens we have today. This is because 2D games use pixel art and this is a fixed resolution image, 3D is different as that is just math, and something that is supposed to be say 10x10 in size can be doubled in size/resolution simply by making that object 20x20 instead (but this also needs more power from the PC as you have quadrupled the amount of polygons needed to render the object now, needing 4x the graphics power as the original resolution game), its very simple math. Also it should be noted that no 2D based system can have it's graphics improved, only 3D systems can 'Upscale' to higher resolutions.
Mame is designed to be as accurate to the original hardware as possible, so it uses the exact resolution and aspect ratio as the original games. So I upgraded to the premum for big box and I noticed that mame games look horrible, and when opening mame? there is almost nothing to change the games graphics, filters nothing.
