While I agree in principle with scotto about both plug seeing the same conditions, I have owned several dirtbikes over the years with two plug heads and I have found myself thankful for the spare plug more times than I can remember.
While I still think it's a waste of money to make parts this nice for a chinagirl, the two plug setup could at least save you a pedal home due to a fouled plug.
This level of craftsmanship and quality on a china motor is like chrome plating a turd in my opinion. When you're done spending, it's still just a shiny turd.
But to each his or her own. I'll use the extra cash to build many, many china girls, some use it to build one really shiny chinagirl.
But in the end, it's all about what kind of turd YOU want.