I foremost think people should have the freedom to bust their nut over resolutions if it makes them cum but personally, I don't see any difference visually in using S-Video to cheap CRT tv with recent mames and a pcb in a real cabinet. Slightly different scanline positions? Is Sherlock Holmes playing with a magnifying glass? It looks the same. In many cases it looks more vibrant because you have color controls on the tv and when you're in an arcade you get what you get.
If scart can slice another frame of input lag over S-Video (can it?) then cool but mame already adds some either way so it's not 100% accurate either way you look at it.