From what I've seen, the mod required to get the SNES cable to work on the N64 cable seemed simple enough. It didn't have any super small soldering points which is what usually turns me off to mods. It's something I might consider if I ever get a 4th cable.
I'm using the Retrovision component cables on my SNES, SMS and Genesis/32x/CD. So far I'm very happy with the setup and quality of the image. I cannot compare it to the "RGB scart to HDMI via converter" method since I have no experience with it, but it is a step up from what I was using previously (s-video for SNES and composite for the two Sega systems).