Higher multiplier means you can get a higher overclock on a board that might have a FSB wall, but otherwise it makes no difference, aside from the FSB wall and also how stable your RAM may be able to perform at lower FSB. Buying cheaper RAM is sometimes a better solution for people so they want to have a higher multiplier.
If yours is stable at 8x then you could look at it as a waste of money I guess... but just be happy you are stable
Although, using a higher multiplier does generate better power savings if you have C1E/SpeedStep enabled because its going from a higher multiplier to the low power multi... For example, on a Q6600 if you leave multiplier at 9 the low power multi is 6, so the savings would be a lot more than a shift from, say, 7 to 6.