Well it's too late now, but I was in a similar situation...
Personally I think the composite on the PC Engine is just fine, but I was getting annoyed with swapping the composite around - especially as my PC Engine ones are flakey (need some new ones I think).
Anyway, after a cable blowout, and replacing my old 360 with an HDMI model, I'm closer to getting a port for everything on the back of my TV;
360 - HDMI
Wii - Component
Core Grafx/Super CD - Phono
SuperGrafx ^ uses same Cable
SNES - RGB scart (when it's working properly)
N64 - ^ same cable
Megadrive - Scart RGB (so need a scart splitter)
PS2 - non RGB scart (only gets used for singstar!)
Dreamcast - VGA, when I get the cable.
The Famicom, if I ever get the AV mod working, will use the phono port too, but I might just stick it on another TV anyway. But that sets me up so that pretty much everything but the PS2 is running at its optimal quality video, should be fairly tidy, and everything just needs to be turned on and switched to the right channel.
I think I might go for one of the crappy RGB switches that route the signal without a switch, just so I don't have to press another button.