(figurative) people whose criticisms are regarded as irrelevant or insignificant (resembling uneducated people who throw peanuts on the stage to express displeasure with a performance)
rearmost or uppermost area in the balcony containing the least expensive seats
Then again, we can only offer you so many suggestions before we open this question up to the folks in the peanutgallery -- so what do you peeps down there think?