I've sandblasted mine before but be very very careful about cleaning them up. Look really good down inside to make sure no sand is wedged in there. You'll have to take a needle to pry some grains out. I also will take a butane torch and heat 'em up real hot.
It really not worth taking the risk with sanding them, take a torch to them, but don't over heat them, just enough to burn off some of the residue, I would only do this once if any, for the cost of a plug its just not worth taking the risk of getting dirt into the plug and then ultimately into the engine