Precious metal electrodes (iridium and platinum) last longer, so will maintain the proper gap for a much longer time. They have allowed new car mfrs to extend plug change recommendations to 100K miles. If platinum-tipped plugs cured a fouling problem, it's probably because they were a slightly hotter heat range.

I'm not sure what, if anything, copper core and Rapid Fire plugs do that other plugs can't. I guess a copper core could reduce resistance, allowing more spark current, but who knows if the performance increase is even measurable?