Not really.

I went the Scart-to-RGB route with my genesis because its stock composite picture is pretty lousy. It ended up costing about 60-70 bucks for the converter and a RGB cable with built in Audio splitter. It was an upgrade well worth it and the picture looks fantastic on a CRT screen.

My SNES was an earlier model so S-video was an option. I picked up the cable and again massive improvement over composite as expected. I picked up an SCART-RGB cable for my SNES and tried it out with little improvement. So little in fact that I don't want to go through the trouble of plugging and unplugging the rather snug SCART cable every time I switch consoles. I really didn't see enough of an improvement to justify the 10 dollar cable over S-video, you might but it really wasn't that dramatic.