A lot of the Max Power car type of magazines test these types of plugs from time to time. They create a cleaner or hotter spark but they provide virtually no increase in power. The main advantage seems to be longer lasting than standard plugs. If anyone can claim to notice a difference (big or small), they're a better man than me. Advertising hype ? I have the platnium type plugs in the VFR, they are certaintly sticking the pace better than standard so I guess the extra outlay was worth it.
Better Smeg than dead